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Index for Section 8 |
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Alphabetical listing for P |
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presto(8)
NAME
presto - Controls and monitors the Prestoserve file system accelerator
SYNOPSIS
/usr/sbin/presto [flags]
DESCRIPTION
The presto command allows you to accelerate file systems, obtain
Prestoserve status, and administer Prestoserve.
If invoked with no flags, presto displays the Prestoserve state (either UP,
DOWN, or ERROR), the number of bytes of nonvolatile memory the Prestoserve
cache is using, how long the cache has been enabled, the write cache
efficiency, and the state of the backup battery or batteries.
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
appropriate disks.
If it detects a disk error during a write back, Prestoserve enters the
ERROR state and disables itself. However, Prestoserve continues to
maintain the integrity of cached data. Some possible disk error conditions
are: the disk drive is write protected or off line, a cable problem
exists, or a bad disk block exists.
Also, if there is insufficient backup battery power, Prestoserve will enter
the ERROR state.
FLAGS
-d [filesystem ...]
Disables Prestoserve and writes the Prestoserve cache data to the
intended disks. Only those file systems specified by filesystem are
disabled. 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 no file systems are specified, all accelerated file systems are
disabled, and the Prestoserve state is set to DOWN.
This flag does not reset Prestoserve statistics.
The -d flag takes effect before the -u or -R flags.
-D [filesystem ...]
Similar to the -d flag, but 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
-F Writes the Prestoserve cache data to the intended disks, but leaves the
cache data intact.
If the flag is used and the Prestoserve state is UP, then the cache
data is written to the intended disks, and the state remains UP. If
the Prestoserve state is DOWN, then there is no data to write to the
disks, and the state remains DOWN. If the state is ERROR, then as much
of the cache data as possible is written to the intended disks.
Note that unlike the -R flag, the data in the Prestoserve cache remains
after it is written to the intended disks.
-h hostname [-pv] [-s size] [-d | -u]
Invokes the specified operations on the remote machine hostname by
using an RPC protocol. The remote machine must be running the
prestoctl_svc daemon to allow the use of the -h flag. The
prestoctl_svc -n flag is required to allow the use of -h with the -s,
-d, and -u administrative flags. See prestoctl_svc(8) for details.
Note
To avoid possible security and performance problems, Digital
strongly recommends against using the -h option. See the
rsh(1) reference page for alternative methods to use for
remote operations.
-l Lists the accelerated file systems and their mount points in a format
similar to the mount command. This flag can be used with either NFS
client or server machines.
-L Lists all local and remote mounted file systems and their mount points
that have been accelerated. Any unusual Prestoserve state for a file
system is displayed after the mount point. The unusual states include:
bounceio
Instead of directly accessing the nonvolatile memory, the file
system's device receives the Prestoserve data only after the data
is first copied to main memory.
disabled
Prestoserve acceleration is not enabled on the file system.
error
An error occurred using the file system, and the Prestoserve cache
data has still not been written successfully to the intended disks.
-p Displays Prestoserve information. The information includes the current
Prestoserve state; the statistics for write, read, and total
operations; and battery status. For example:
# /usr/sbin/presto -p
dirty = 52, clean = 7, inval = 0, active = 2
count hit rate clean hits dirty hits allocations passes
write: 1516 65% 0 989 511 15
read: 8 0% 0 0 0 8
total: 1524 65% 0 989 511 23
state = UP, size = 0x7e000 bytes
statistics interval: 00:00:13 (13 seconds)
write cache efficiency: 66%
All batteries are ok
The current Prestoserve statistics account for all Prestoserve buffers.
A dirty buffer contains a disk block image that has not been written to
disk. A clean buffer contains a valid disk block image that has been
written to disk. An inval buffer does not presently contain a disk
block image. An active buffer is currently in transition to disk,
meaning that a write operation has started but has not completed on
that buffer.
For each Prestoserve cache read or write operation, Prestoserve
increments a counter, as follows:
·
The clean hits counter shows the number of hits (block matches) on
the clean buffers.
·
The dirty hits counter shows the number of hits on the dirty buffers.
Each dirty hit on a write represents a physical disk write that was
avoided entirely, while a dirty hit on a read represents the same
condition for a disk read.
·
The allocations counter shows the number of new buffers that had to
be allocated for disk block images.
·
The passes counter shows the number of I/O operations that
Prestoserve passed directly to the real device driver.
In addition, for each Prestoserve cache read or write operation, the
presto -p command displays the count, which is the sum of the four
counters explained previously; the hit rate percentage, which is the
ratio of clean hits and dirty hits to the total count and which
indicates the effectiveness of the Prestoserve cache; and the write
cache efficiency percentage, which is computed from the ratio of write
dirty hits to the number of writes copied into the Prestoserve cache.
The presto -p command also displays information about the Prestoserve
battery state. The command displays the battery state as ok, low, or
disabled.
Some processors support chargeable batteries and use self tests to
determine if a battery needs charging. If you use the presto -p
command on a machine that supports chargeable batteries and is running
Prestoserve locally, the battery state can also be in self test or is
charging. Note that if you use the -p flag with the -h flag (or if you
use the dxpresto command, batteries that are being self-tested or
charged will be displayed as disabled.
-R Writes as much of the Prestoserve cache data as possible to disk,
discards the data it could not write, purges all the Prestoserve
buffers, and sets the Prestoserve state to DOWN.
Unlike the -d flag, the -R flag discards the Prestoserve cache data
that could not be written to disk and resets the statistics
information. The flag is useful when Prestoserve cache data is not
needed or if you cannot get Prestoserve out of the ERROR state.
Caution
Take care when using the -R flag, because it destroys
Prestoserve cache data.
The -R flag takes effect before the -u flag.
-s size
Sets the size of the Prestoserve cache to size bytes. The size can be
specified using the decimal or hexadecimal conventions. For example,
both 262144 and 0x40000 represent 256 Kbytes.
If the -s flag is used 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.
You may want to use the -s flag to determine how Prestoserve performs
with a reduced amount of nonvolatile memory. Note that the size of the
Prestoserve cache cannot be larger than the default maximum size. If
you specify a size that is larger than the default maximum size, the
default maximum size is used.
-u [filesystem ...]
Sets Prestoserve state to UP, and enables acceleration.
Only those file systems specified by filesystem are 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 no file systems are specified, all local writable file systems that
are mounted will have Prestoserve enabled. File systems that are
presently accelerated will remain accelerated.
If Prestoserve state was ERROR, Prestoserve attempts to write any
blocks that are in the cache to disk to ensure that the previous error
condition has been corrected.
-U [filesystem ...]
Similar to the -u flag, but 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
-v Specifies verbose mode. This flag prints extra information to standard
output. The information can be used for debugging purposes.
FILES
/dev/pr0
RELATED INFORMATION
prestoctl_svc(8), dxpresto(8X), presto(7), prestotab(4), prestosetup(8)
Guide to Prestoserve