3 Prestoserve Administration

This chapter explains how to administer the Prestoserve software. It explains how to select file systems to accelerate and how to use the presto and dxpresto commands to perform the administrative procedures for the day-to-day operation of Prestoserve. It also describes how to check to determine if Prestoserve is working properly.

3.1 Prestoserve Operation

The following sections explain how Prestoserve operates. It describes the Prestoserve buffers and states.

3.1.1 Prestoserve Buffer Management

Prestoserve is implemented as a pseudodevice driver and uses nonvolatile memory to cache synchronous write requests. Write requests are written synchronously to the Prestoserve cache buffers; as the cache fills, old data is written asynchronously to the appropriate disks.

Prestoserve is interposed between other disk drivers and the rest of the Digital UNIX kernel. Stubs replace the original driver's entry points in the device switch tables. Whenever Prestoserve needs to perform actual I/O (for example, when the data in the cache needs to be written to disk), it uses the real device driver routines.

Buffers in the Prestoserve cache undergo several phases or states. The buffer transition diagram is roughly as follows:

inval -> dirty -> active -> clean -> dirty

The following list describes the buffer states:

inval An invalid buffer does not presently contain a disk block image.

dirty A dirty buffer contains a valid disk block image that has not yet been written to disk.

active An active buffer is currently in transition to the disk, which means that a write operation has started, but it has not been completed on that buffer.

clean A clean buffer contains a valid disk block image that has been written to disk.

3.1.2 Prestoserve States

The Prestoserve buffer cache is similar to a disk because it contains data. At appropriate times, the data is written to the actual disks. The Prestoserve driver tries to ensure that data is not lost. When a failure occurs, the driver does not discard cache data unless explicitly requested to do so by the system administrator.

Prestoserve is always in one of three states: UP (enabled), DOWN (disabled), or ERROR (error). When the Prestoserve state is UP, Prestoserve improves I/O performance to accelerated file systems by caching synchronous disk write operations to nonvolatile memory. When the Prestoserve state is DOWN, all I/O requests are passed to the actual devices.

Whenever Prestoserve makes a state transition from UP to DOWN, all Prestoserve buffers are successfully flushed (that is, the data is written to disk) and invalidated. If there are dirty buffers in the Prestoserve cache when the system is rebooted, they are flushed, and Prestoserve enters the DOWN state unless an error occurred during the flushing. Some possible disk errors are: the disk drive is write protected or off line, a cable problem exists, or a bad disk block exists.

Note
Because the Prestoserve state is DOWN after a reboot, you may want to set up Prestoserve so that file systems are automatically enabled when the system starts up. Refer to Chapter 2 for information about automatically acclerating file systems.

If an error occurs, Prestoserve enters the ERROR state. When in the ERROR state, the Prestoserve cache is effectively read-only until the error condition is cleared; then, Prestoserve enters the DOWN state. After you fix the disk error, use the presto -u or the presto -U command to verify that the error is corrected. If there are no disk errors, the remaining cached data is written to disk and Prestoserve is reenabled. Refer to Section 3.2.1 for more information about the presto -u and presto -U commands.

The commands that use the reboot system call cause Prestoserve to enter the DOWN state if all dirty buffers can be successfully flushed. If the buffers cannot be successfully flushed, Prestoserve enters the ERROR state. Commands that are used to reboot the system include the halt, shutdown, and reboot commands. Refer to Chapter 4 for more information on recovering from the ERROR state.

3.2 Managing Prestoserve

The following sections describe how to manage the Prestoserve software. They describe how to select file systems to accelerate, perform remote Prestoserve administration, display status, and manage the Prestoserve buffer cache.

The presto command is used to administer Prestoserve. The dxpresto command is used to perform some administrative tasks and also to monitor Prestoserve.

The presto command can perform the following administrative tasks:

Enable and disable file system acceleration
Administer Prestoserve on remote systems
Display information about the accelerated file systems
Display information about Prestoserve state and buffer status
Reset Prestoserve
Write the contents of the Prestoserve cache to disk
Change the size of the Prestoserve cache
Display Prestoserve troubleshooting information

Refer to presto(8), dxpresto(8X), and the following sections for more information.

3.2.1 Accelerating File Systems

Prestoserve can accelerate all mounted file systems on a server, regardless of how many disks or controllers are involved. You should accelerate file systems that receive many synchronous write requests. Read-only file systems do not generate synchronous write requests; therefore they are usually not accelerated.

The following list describes some of the types of file systems that may derive benefits from Prestoserve:

File systems that are accessed through the NFS (because many requests for such files are synchronous)
File systems that are used heavily for synchronous I/O
Local file systems (because some operations, such as creating or removing a file, generate synchronous writes)
Remote swapping done to NFS files may benefit from Prestoserve

Prestoserve maintains full block and raw disk semantics. The performance benefits of Prestoserve are not available to raw character device disk partitions. Raw character device reads and writes will flush blocks that are in the Prestoserve cache to disk.

You can use the presto command with the -u or -U option to set the Prestoserve state to UP and enable acceleration on the specified file systems. The -U option sets the Prestoserve state to UP only if the specified directory is the root of a mounted file system. Otherwise, the following message is displayed:

   presto: directory is not a file system root

Note that you can set up Prestoserve to automatically accelerate mounted file systems when the system starts up by specifying the appropriate run-time variables in the /etc/rc.config file and including the file systems in the /etc/prestotab file. Otherwise, you will have to manually accelerate the file systems each time you reboot. Refer to Chapter 2 for more information.

The presto command with the -u or -U option has the following syntax:

presto -u | -U [ filesystem ... ]

Only those file systems specified by the filesystem variable will have Prestoserve enabled. You specify filesystem as a directory mount point (for example, /usr). Do not specify a block device because some functional subsystems, such as the Advanced File System (advfs), can map more than one block device to a mount point. If filesystem is not specified, all local writable file systems that are mounted will have Prestoserve enabled. File systems that are presently accelerated will remain accelerated.

If the Prestoserve state was DOWN, the -u and -U options also reset the Prestoserve statistics and buffers to their initial values. If Prestoserve was in the ERROR state, Prestoserve attempts to write to disk any blocks that are still in its cache to make sure that the error has been corrected.

If you mount a local file system using the mount command after the system is running in multiuser mode, you must use the presto -u or presto -U command and specify the mount point to accelerate the file system.

Note
When you use the presto command option -h with the -u or -U option, Prestoserve is enabled only on those remote file systems that were previously accelerated and have not been disabled by the remote host's administrator.

The following examples enable Prestoserve on all mounted read/write local file systems, on all previously accelerated file systems on a remote host, on a specific mounted file system, and on a directory mount point that is the root of a mounted file system, respectively:

# presto -u
# presto -h mmate3 -u
# presto -u /rz1g
# presto -U /usr

3.2.2 Disabling File System Acceleration

You can use the presto command with the -d or -D option to stop Prestoserve acceleration and write any Prestoserve cache data to disk.

The -D option is similar to the -d option, but it sets the Prestoserve state to DOWN only if the specified directory is the root of a mounted file system. Otherwise, the following message is displayed:

    presto: directory is not a file system root

The presto command with the -d or -D option has the following syntax:

presto -d | -D [ filesystem ... ]

Only those file systems specified by the filesystem variable are disabled. You specify filesystem as a directory mount point (for example, /usr). If filesystem is not specified, all accelerated file systems are disabled, and the Prestoserve state is set to DOWN.

Note that the -d and -D options do not reset Prestoserve statistics, and they take effect before the -u, -U, or -R option.

The following command disables the mounted file system /usr:

# presto -d /usr

3.2.3 Administering Prestoserve from a Remote System

You can use the presto command with the -h option to administer Prestoserve on a remote machine by using a Remote Procedure Call (RPC) protocol. You can combine the -h option with all the presto command options except -R and -L.

The presto -h command has the following syntax:

presto -h hostname

The hostname variable specifies the name of the remote host.

The remote machine must be running the prestoctl_svc Prestoserve control daemon to allow remote operations on that host. In addition, the remote host must be running prestoctl_svc with the -n option to allow the use of the -u, -U, -d, -D, and -s administrative options on the remote host. Refer to Chapter 2 and to prestoctl_svc(8) for more information.

You can automatically start the prestoctl_svc daemon when the system starts up by setting the PRESTO_SVC_ENABLE and PRESTO_SVC_ANY run-time variables in the /etc/rc.config file on the remote host. This enables the remote host to use the presto -h command each time it starts up. Refer to Chapter 2 for more information.

3.2.4 Displaying the Status of File Systems

You can use the presto command with the -l and -L options to display information about the accelerated file systems.

The -l option lists the accelerated file systems and their mount points in a format that is similar to the mount command. The -l option also displays NFS file systems if the server is running the prestoctl_svc daemon and if the NFS file systems have been accelerated.

For example:

# presto -l

/dev/rz0a on /
/dev/rz1g on /usr/staff
/dev/rz2a on /rz2a
/dev/rz2g on /rz2g
mmate3:/usr/staff on /mmate3

The -L option displays NFS file systems if the server is running the prestoctl_svc daemon. In addition, the -L option displays any unusual Prestoserve state for the file systems. The unusual states include the following:

bounceio Instead of directly accessing the Prestoserve cache, the disk device receives the data only after it is first copied to main memory.

disabled The file system is not accelerated.

error An error occurred using the file system, and the data has still not been written successfully.

For example:

# presto -L

/dev/rz0a on /
/dev/rz0g on /usr (disabled)
/dev/rz1a on /rz1a
/dev/rz1g on /usr/staff
/dev/rz2a on /rz2a
/dev/rz2g on /rz2g
mmate3:/usr/staff on /mmate3
sunk:/home on /sunk (bounceio)

3.2.5 Displaying the Prestoserve State and Buffer Status

If invoked with no options, the presto command displays the Prestoserve state (either UP, DOWN, or ERROR), the number of bytes of nonvolatile memory the Prestoserve cache is using, the length of time the cache has been enabled, the write cache efficiency, and the current condition of the batteries.

The following is an example of the presto command with no options specified:

# presto

state = DOWN, size = 0x7e000 bytes
statistics interval: 00:00:00  (0 seconds)
write cache efficiency: 0%
All batteries are ok

You can use the presto command with the -p option to display additional information about the current Prestoserve state and the statistics for write, read, and total operations. The information displayed by the -p option is similar to the information displayed by the dxpresto command.

Example 3-1 shows an example of the presto -p command and its output. A description of the output follows the example.

Example 3-1: Prestoserve Status


# 
presto -p

dirty = 0, clean = 61, inval = 0, active = 0
        [1]        [2]          [3]          [4]           [5]           [6]
       count  hit rate  clean hits  dirty hits  allocations  passes
write:  1188     65%       595         182          93        318
 read:     6      0%         0           0           0          6
total:  1194     65%       595         182          93        324
state = UP, size = 0x7e000 bytes
statistics interval: 00:00:35  (35 seconds)
write cache efficiency: 21%      [7]
All batteries are ok         [8]

For each cache read or write operation, Prestoserve increments a counter. A hit occurs when a requested block is matched to a block in a buffer. The previous example shows the following information:

The count specifies the sum of the clean hits, dirty hits, allocations, and passes counters. [Return to example]
The hit rate percentage is the ratio of the clean hits and dirty hits counters to the count.
Note
The hit rate percentage for Prestoserve cache writes indicates the effectiveness of the Prestoserve cache. If the number of read operations is high in proportion to the total count of read and write operations (75% or more), you may improve system performance by increasing the amount of main memory allocated to the file system buffer cache.
[Return to example]
The clean hits counter specifies the number of hits on the clean buffers. [Return to example]
The dirty hits counter specifies the number of hits on the dirty buffers. Each dirty hit represents a physical disk write that was avoided entirely. [Return to example]
The allocations counter specifies the number of new buffers that had to be allocated for disk block images. [Return to example]
The passes counter specifies the number of I/O operations that Prestoserve passed directly to the real device driver. [Return to example]
The write cache efficiency, percentage is computed from the ratio of write dirty hits to the number of writes copied into the Prestoserve cache (write count - write passes). [Return to example]
The battery state indicates the condition of the batteries. In general, the battery state can be OK, low, or disabled, but some processors support chargeable batteries and use self-tests to determine if a battery needs charging. If your processor supports chargeable batteries and is running Prestoserve locally, the battery state can also be specified as in self-test or is charging.
Note that if you use the -p option with the -h option (or if you use the dxpresto command), batteries that are being self-tested or charged will be displayed as disabled. [Return to example]

The following is an example of the presto command with the -l and the -p options specified:

# presto -lp

dirty = 54, clean = 3, inval = 0, active = 4
       count hit rate clean hits dirty hits allocations passes
write:  1236      65%          0        808         421      6
 read:     2       0%          0          0           0      2
total:  1238      65%          0        808         421      8
state = UP, size = 0x7e000 bytes
statistics interval: 00:00:10  (10 seconds)
write cache efficiency: 66%
All batteries are ok
/dev/rz0a on /
/dev/rz0g on /usr
/dev/rz1a on /rz1a
/dev/rz1g on /usr/staff
/dev/rz2c on /rz2c
mmate3:/usr/staff on /mmate3
sunk:/home on /sunk

The following example shows the output of the presto command when you use the -h option with the -p option:

# presto -h mmate3 -p

mmate3:
dirty = 0, clean = 0, inval = 126, active = 0
       count hit rate clean hits dirty hits allocations passes
write:    46      61%          0         28          17      1
 read:     0     100%          0          0           0      0
total:    46      61%          0         28          17      1
state = DOWN, size = 0xffc00 bytes
statistics interval: 00:00:01  ( seconds)
write cache efficiency: 62%
All batteries are ok

3.2.6 Using dxpresto to Administer and Monitor Prestoserve

The dxpresto command starts the worksystem software application that graphically displays information about Prestoserve in a window. You can use the command to monitor Prestoserve activity. It also allows you to enable or disable Prestoserve on machines that allow that operation.

You can invoke the dxpresto command on a machine running Prestoserve to obtain that machine's Prestoserve information, or you can specify a remote host running Prestoserve to obtain that host's Prestoserve information by using remote procedure calls.

Note
Because dxpresto is a worksystem software application, the DISPLAY environment variable must be set to a machine that is running the worksystem software. See putenv(3) for information on setting environment variables.

The dxpresto command displays the following information:

Prestoserve state
Number of kilobytes of nonvolatile memory that the Prestoserve cache is utilizing
Amount of time that Prestoserve has been enabled
Battery condition
Current state of all the Prestoserve buffers
History of Prestoserve writes per second
History of Prestoserve cache hits per second
Prestoserve statistics for write, read, and total operations
Prestoserve and dxpresto command error messages

The dxpresto command also allows you to modify the displayed information by:

Changing the name of the system to be monitored
Changing the Prestoserve state to Enabled (UP) or Disabled (DOWN)
Changing the interval of time between Prestoserve queries
Displaying the Prestoserve statistics for write, read, and total operations since Prestoserve was last enabled
Displaying Prestoserve statistics for write, read, and total operations since Prestoserve was last queried
Displaying Prestoserve statistics for write, read, and total operations since a specific time

The dxpresto command has the following syntax:

/usr/sbin/dxpresto [ hostname ]

The hostname variable specifies the name of the machine you want to monitor; this machine must be running the Prestoserve software. If you do not specify the hostname variable, the local machine running the Prestoserve software is monitored. If the hostname variable is not specified and the local machine is not running the Prestoserve software, the dxpresto window opens but is not functional until you enter the name of a host running the Prestoserve software in the Host field in the dxpresto window. See dxpresto(8X) for more information.

Note
To use the dxpresto command to monitor a machine's Prestoserve activity, the prestoctl_svc daemon must be running on that machine. Refer to Chapter 2 for information on the prestoctl_svc daemon.

An example of the dxpresto command is as follows:

# dxpresto tyres

Figure 3-1 shows a dxpresto window.

Figure 3-1: dxpresto Window

Figure 3-1 shows the following:

Host: This field shows the host that you are monitoring. You can type another name in the field and press the Return key to monitor that host.

Presto State: These buttons show the Prestoserve state, either Enabled, Disabled, or Error. If the machine being monitored is running the prestoctl_svc daemon with the -n option, you can change the machine's Prestoserve state to either Enabled or Disabled. You cannot change an Error state; contact your Digital Customer Services representative if an Error state occurs.

Sample Interval: This slider shows the interval of time between Prestoserve queries; it allows you to change that interval. When you invoke the dxpresto command, the default Sample Interval is 5; therefore Prestoserve information is gathered every 5 seconds. If you want Prestoserve queried more often, move the slider to the left and click on MB1 until 2 appears for example; Prestoserve is then queried every two seconds.

Time since last Enable: This field shows the time since Prestoserve was last enabled. The time is displayed in hours, minutes, and seconds and total number of seconds.

Batteries: These graphics show the state of the Prestoserve backup battery system. An intact battery with the word ok indicates that the battery has sufficient power. An intact battery with the word low indicates that the battery's power is low. A broken battery indicates that the battery is disabled. Prestoserve goes into the ERROR state when the backup battery power falls below a minimum amount. Refer to your hardware documentation to determine the minimum amount of backup battery power. Contact your hardware Field Service representative if a battery has insufficient power or is disabled.

Size: This field displays the number of kilobytes of nonvolatile memory that the Prestoserve cache is utilizing. Note that Prestoserve can utilize less than the default maximum size of its Prestoserve cache if you changed the cache size with the presto -s command.

Display Cache Utilization: These buttons allow you to display graphs that demonstrate how the Prestoserve cache is being utilized.

Display Cache Statistics: These buttons allow you to display the cache statistics table.

Exit: This button allows you to exit the dxpresto window.

Message bar: This area at the bottom of the window displays informational and error messages for the dxpresto command and for Prestoserve. For example, if the prestoctl_svc daemon with the -n option is not running on the machine you are monitoring, then a message is displayed indicating that changes to Prestoserve operation are not allowed.
Error messages, such as those indicating RPC communication failure, are displayed on the terminal from which you invoked dxpresto.

Figure 3-2 shows an example of the dxpresto window with both the Display Cache Utilization graphs and the Display Cache Statistics table displayed. The example shows the Writes per second and Hits per second trend line graphs. Each point in the horizontal axis of each graph represents a sample time interval as determined by the Sample Interval slider; the maximum number of samples that can be shown is 210. When you reach the maximum number of samples, the graph shifts to the left so you can see at least the last 105 samples, which is half the maximum number of samples. If you choose 5 in the Sample Interval slider, Prestoserve is queried every 5 seconds; therefore it takes 1050 seconds (5 x 210) to obtain the maximum of 210 samples.

The vertical axis shows the average number of writes performed per second within the sample time interval. For example, if you choose 2 in the Sample Interval slider, Prestoserve is queried every 2 seconds, and each point in the graph shows the average number of writes performed within the interval of 2 seconds. If the graph shows that an average of 5 writes per second were performed within 2 seconds, Prestoserve actually performed 10 writes within those 2 seconds.

If you change hosts, each graph displays a vertical line of dashes to distinguish the new host's information from the previous host's information.

Figure 3-2: Expanded dxpresto Window

Figure 3-2 shows the following:

Current Buffer Status: This bar graph shows how the Prestoserve cache operations are distributed among the Prestoserve buffer states, which are described in Section 3.1.1. The vertical axis shows the maximum number of objects or disk blocks that the entire Prestoserve cache can contain. The sum of the four bars is the total number of buffers used in the Prestoserve cache. Note that the size of the Prestoserve cache can be changed by using the presto -s command. See Section 3.3.3 for more information.

Writes per second: This trend line graph shows a recent history of the average number of writes per second over the time intervals that are determined by the Sample Interval slider.

Hits per second: This trend line graph shows a recent history of the average number of Prestoserve cache hits per second over the time intervals that are determined by the Sample Interval slider. The Prestoserve cache hits represent the total number of clean and dirty read and write hits.

Since last Enable: This button allows you to display Prestoserve statistics since Prestoserve was last enabled. This is useful when you want to determine how Prestoserve performs over a long period of time.

Since last Sample: This button allows you to display the Prestoserve statistics for each sample time interval as determined by the Sample Interval slider. If no Prestoserve activity occurs during the time interval, the numbers in the statistics table remain at zero. For example, if the Sample Interval slider is set to 5 and the Since last Sample button is enabled, the statistics table shows the Prestoserve statistics for each interval of 5 seconds.

Since last Zero: This button allows you to display Prestoserve statistics since you clicked on the Zero button. This button allows you to determine how Prestoserve performs over a specific period of time.

Zero: This button sets the numbers in the table to zero, allowing you to specify a time reference for the Prestoserve statistics table. At a later time, you can click on the Since last Zero button to display the Prestoserve statistics since you clicked on the Zero button.

Write Cache Efficiency: This field shows the ratio of write dirty hits to the number of writes copied into the Prestoserve cache.

Prestoserve statistics table: This table is similar to the information that is displayed when you use the presto -p command. For each Prestoserve cache read or write operation, Prestoserve increments an appropriate counter. The table shows the following:

count: Specifies the sum of the clean hits, dirty hits, allocations, and passes

hit rate percentage: Specifies the ratio of clean hits and dirty hits to the total count

clean hits: Specifies the number of hits on the clean buffers

dirty hits: Specifies the number of hits on the dirty buffers (each dirty hit represents a physical disk write that was avoided entirely)

allocations: Specifies the number of new buffers that had to be allocated for the disk block images

passes: Specifies the number of I/O operations that Prestoserve passed directly to the actual device driver

3.3 Handling the Prestoserve Cache

The following sections describe how to write the contents of the cache to disk, how to reset Prestoserve and clear the cache, and how to change the size of the cache.

3.3.1 Writing the Contents of the Cache to Disk

You can use the presto command with the -F option to write the contents of the Prestoserve cache to the available disks but keep the contents of the cache intact.

If the -F option is used and the Prestoserve state is UP, the contents of the cache are written to disk, and the state remains UP. If the Prestoserve state is DOWN, then there is nothing to write to disk, and the state remains DOWN.

If the Prestoserve state is ERROR, as much of the contents of the cache as possible is written to disk. Note that, unlike the -R option, the data in the cache remains after it is written to disk. The state remains ERROR until all the cache data is successfully written to disk. Note that if you cannot write all the cache data to disk and the state remains ERROR, you can use the presto -R command to reset Prestoserve, clear the cache, and set the state to DOWN.

The presto -F command can be used to flush dirty Prestoserve buffers to a disk that was temporarily disabled. For example, if a disk is powered down or disconnected from a bus, the Prestoserve cache could enter the ERROR state. When the disk is again available, you can use the presto -F command to move the cache data to disk and change the Prestoserve state from ERROR to UP.

3.3.2 Resetting Prestoserve and Clearing the Cache

If you are unable to clear the contents of the Prestoserve cache and write the data to disk, you can force Prestoserve out of the ERROR state. You reset Prestoserve and clear the cache by using the presto command with the -R option. The -R option writes as much of the Prestoserve cache data as possible to the appropriate disks, discards the data it cannot write, purges all Prestoserve buffers, and sets the Prestoserve state to DOWN.

Note
The -R option clears the Prestoserve cache by writing the data to the appropriate disks if possible. If a disk is unavailable, the data from the cache is lost, so you should use the option carefully.

Unlike the -d, -D, and -F options, the -R option discards the Prestoserve cache data that it could not write to disk. The option is useful when cache data is not needed. Note that the -R option takes effect before the -u or -U option.

In the following example, the -R option changes the Prestoserve state to DOWN:

# presto -Rp

dirty = 0, clean = 61, inval = 0, active = 0
       count hit rate clean hits dirty hits allocations passes
write:  1188      65%        595        182          93    318
 read:    10       0%          0          0           0     10
total:  1198      65%        595        182          93    328
state = DOWN, size = 0x7e000 bytes
statistics interval: 00:00:00  (0 seconds)
write cache efficiency: 0%
All batteries are ok

3.3.3 Changing the Cache Size

You can use the presto command with the -s option to change the size of the Prestoserve cache to the specified number of bytes. The size of the Prestoserve cache should be specified in the Prestoserve hardware documentation or product description. The presto -s command has the following syntax:

presto -s size

You can specify the size variable using decimal or hexadecimal conventions. For example, both 262144 and 0x40000 represent 256 kilobytes.

You may want to use the -s option to determine how Prestoserve performs with a reduced amount of nonvolatile memory. Note that the size of the Prestoserve cache cannot exceed the default maximum size; the default maximum size is used if you specify a size larger than this size. Refer to your processor hardware documentation for information about the default maximum size of the Prestoserve cache.

If you specify the -s option and the current Prestoserve state is UP, the state is set to DOWN, the Prestoserve cache is resized, and the state is set to UP.

For example, the following command changes the size of a Prestoserve cache to 512 kilobytes:

# presto -h mate -s 0x80000 -p

mate:
dirty = 119, clean = 3, inval = 0, active = 4
       count hit rate clean hits dirty hits allocations passes
write:  1350      66%          0        893         455      2
 read:     0     100%          0          0           0      0
total:  1350      66%          0        893         455      2
state = UP, size = 0x80000 / 0xffc00 bytes
statistics interval: 00:00:00  (0 seconds)
write cache efficiency: 33%
All batteries are ok

3.4 Displaying Debugging Information

You can use the presto command with the -v option to obtain information that you can use to debug Prestoserve operation. The -v option is used with other presto command options and displays extra information to standard output.

3.5 Checking Prestoserve

The system administrator can check to determine if Prestoserve is working properly by performing the following steps:

Log in to the server as root and disable Prestoserve:
# presto -d

See Chapter 3 for information on the presto command.
Log in to a client system and mount one of the server's file systems that is exported by the NFS and that has at least as much available space as the size of the client's \/vmunix file or some other large file. Use a mount point where the client can create files. The following example uses /usr/tmp as a mount point; the commands establish the client's level of performance without Prestoserve:
client% mount server:/usr/tmp /mnt
client% cd /mnt
client% /bin/time cp /vmunix bigfile
```
  34.1 real         0.0 user         1.1 sys
```
client% rm bigfile
Enable Prestoserve on the server:
server# presto -u
Establish the client's level of performance with Prestoserve:
client% /bin/time cp /vmunix bigfile
```
 10.3 real         0.0 user         1.1 sys
```
client% rm bigfile
client% cd /
client% umount /mnt

The real time reported by the commands in step 4 is expected to be about one third of (or about three times faster than) the real time reported by the commands in step 2 while Prestoserve was disabled. Your improvement will vary, but the expected range is between three and five times faster with Prestoserve enabled. If you see much less than a factor of three, make sure that all the other clients are idle and that your network is not being used by others at this time.

`inval`	An invalid buffer does not presently contain a disk block image.
`dirty`	A dirty buffer contains a valid disk block image that has not yet been written to disk.
`active`	An active buffer is currently in transition to the disk, which means that a write operation has started, but it has not been completed on that buffer.
`clean`	A clean buffer contains a valid disk block image that has been written to disk.

`bounceio`	Instead of directly accessing the Prestoserve cache, the disk device receives the data only after it is first copied to main memory.
`disabled`	The file system is not accelerated.
`error`	An error occurred using the file system, and the data has still not been written successfully.