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Index for Section 7 |
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Alphabetical listing for P |
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presto(7)
NAME
presto - the Prestoserve pseudodevice driver
SYNOPSIS
#include <sys/presto.h>
#include <sys/prestoioctl.h>
pseudo-device presto
DESCRIPTION
The Prestoserve pseudodevice driver presto caches synchronous writes in
nonvolatile memory. Prestoserve causes synchronous writes to be performed
at memory speeds, rather than at disk speeds. Synchronous writes that
result in Prestoserve cache hits do not perform the earlier physical disk
writes, because only the last write is actually performed by Prestoserve.
Therefore, 50% to 65% of all the physical disk write operations are
avoided, because every sequential NFS write to a file also causes the inode
and the indirect block to be synchronously written.
The presto driver is layered on other disk drivers, and it intercepts the
other drivers' I/O requests by replacing the entry points of the original
driver in the bdevsw and cdevsw tables. The presto driver caches the
intercepted synchronous write requests in the Prestoserve cache's
nonvolatile memory. When Prestoserve needs to perform actual I/O, it calls
the original driver's entry points to perform the I/O. A modified form of
Least Recently Used (LRU) replacement determines when the Prestoserve cache
data needs to be written to the intended disks.
An accelerated disk device (one that has the presto pseudodevice driver
layered on top of its driver), uses the same major and minor devices that
it used before it was accelerated.
The Prestoserve nonvolatile memory must be found at boot time in order for
Prestoserve to perform its write-caching function. In addition,
Prestoserve must pass diagnostic tests, and there must be sufficient backup
battery power to guarantee a reasonable amount of cache data stability
(measured in days or weeks) in the event of a power or hardware failure.
If the Prestoserve nonvolatile memory is not found or if there is not
enough backup battery power, then the disks are not accelerated; however
they can be opened and used as usual. In this case, the presto driver
simply passes all I/O requests directly through to the appropriate device.
Operation
When Prestoserve is in the PRUP state, it caches all synchronous write
requests for enabled file systems to the presto driver in nonvolatile
memory and writes the Prestoserve cache data asynchronously to the intended
disks.
When Prestoserve is in the PRDOWN state, there is no data in the
Prestoserve cache, no data is put into the Prestoserve cache, and all disk
requests are passed directly to the real disk driver.
When Prestoserve is in the PRERROR state, the data in the Prestoserve cache
can not be written to the intended disks because of a disk, system, or
hardware error.
When the system is shut down normally by using the reboot system call from
the shutdown, halt, or reboot command, the Prestoserve cache data is
written to the intended disks, and Prestoserve enters the PRDOWN state.
This allows you to fix any system or disk error or to upgrade or change
your system without losing the data in the Prestoserve cache or corrupting
your disks.
If your system was shut down without following normal shutdown procedures,
and you reboot the system, any data in the Prestoserve cache is written to
the intended disks, if possible. If the data is successfully written to
the intended disks (and if the nonvolatile memory and backup battery passed
the diagnostic tests), Prestoserve enters the PRDOWN state. If an error
occurs, Prestoserve enters the PRERROR state.
Note
Data can exist in the Prestoserve cache after you reboot the system only in
the event of a previous power failure, disk device error, or kernel crash
that resulted from a software or hardware problem.
If an error from a disk device occurs or if the backup battery power is
insufficient, Prestoserve writes the cache data to the intended disks, if
possible, and enters the PRERROR state. When Prestoserve is in the PRERROR
state, new data that is written to a block not found in the Prestoserve
cache is passed directly to the real disk driver. If new data is written
to a block that is found in the cache, Prestoserve replaces the existing
block and attempts to write the block to the real disk driver to determine
if the error condition on that block still exists. If the write is
successful and if all the Prestoserve cache data can be written to the
intended disks, Prestoserve leaves the PRERROR state.
The Prestoserve cache never discards data without being explicitly told to
do so by using a PRRESET ioctl command. This can be done by using the
presto -R command. This command should only be used when there is a fatal
disk error and when the data is not important.
ioctl Commands
The presto pseudodevice driver does not intercept ioctl commands; they go
directly to the actual disk driver. The following ioctl commands can be
performed on the Prestoserve control device /dev/pr0. Some ioctl commands
affect all of Prestoserve operation, while others only affect a particular
accelerated file system.
PRGETSTATUS
The argument to ioctl is a pointer to a presto_status structure, which
contains battery status information, Prestoserve state, current and
maximum nonvolatile memory sizes, and various Prestoserve statistics.
PRNGETSTATUS
The argument to ioctl is a pointer to a presto_status structure, which
contains extended chargeable battery status information, Prestoserve
state, current and maximum nonvolatile memory sizes, and various
Prestoserve statistics.
PRSETSTATE
The argument to ioctl is a pointer to an int. The int can be either
PRUP to enable Prestoserve or PRDOWN to disable Prestoserve. When a
system reboots, Prestoserve is in the PRDOWN state and must be
explicitly enabled by an ioctl. You enable Prestoserve by using the
presto -u command. You can also automatically enable Prestoserve by
specifying the appropriate run-time variables in the /etc/rc.config
file and specifying file systems in the /etc/prestotab file. The
prestosetup command provides you with an interactive facility to set
up Prestoserve. When Prestoserve goes from the PRDOWN state to the
PRUP state, the Prestoserve I/O statistics are reset. When
Prestoserve goes from the PRUP state to the PRDOWN state, all the
Prestoserve buffers are written to the intended disks, and the buffers
are invalidated.
PRSETMEMSZ
The argument to ioctl is a pointer to an int. This int is the size in
bytes of the Prestoserve nonvolatile memory to be used. This size
cannot be larger than the maximum size reported in the presto_status
structure.
PRRESET
The argument to ioctl is ignored. Like the PRSETSTATE ioctl, PRRESET
sets the Prestoserve state to PRDOWN, but it also reinitializes all of
nonvolatile Prestoserve memory. If Prestoserve was in the PRERROR
state and some Prestoserve buffers could not be written to the
intended disks because of disk I/O errors, the data in the buffers is
lost. This is the only method you can use to force Prestoserve to
discard data that cannot be written to disk, and it can be
accomplished by using the presto -R command.
PRFLUSH
The argument to ioctl is ignored. All the data in the Prestoserve
buffers is written to the intended disks, but the buffers are not
invalidated. This command can be used by a daemon that flushes the
cache periodically to minimize the risk to data in the event of a
catastrophic failure. The cache data can be flushed to the intended
disks by using the presto -F command.
PRGETUPRTAB
The argument to ioctl is a pointer to a struct uprtab. On input, the
upt_bmajordev and upt_unit fields specify the block device major
number and unit number of the device whose struct uprtab should be
returned. The upt_bmajordev and upt_unit fields are set to NODEV ,
which is defined in the header file <sys/param.h>, if the requested
device does not exist or if it is not accelerated. The struct uprtab
contains a upt_enabled field that is a bit vector indexed by a
partition number and that indicates whether the partition has
Prestoserve caching enabled.
PRNEXTUPRTAB
The argument to ioctl is a pointer to a struct uprtab. This ioctl
returns the struct uprtab for the accelerated device with the smallest
(block device major number, unit number) pair that is greater than the
upt_bmajordev and upt_unit fields of the struct uprtab argument. This
allows each accelerated device's struct uprtab to be retrieved
sequentially by specifying the previous device's (block device major
number, unit number) pair. To get the first accelerated device's
struct uprtab, set the upt_bmajordev and upt_unit fields to NODEV .
Use the same struct uprtab that was returned on the previous call for
the next call. When the upt_bmajordev and upt_unit fields of the
struct uprtab argument are greater than or equal to the last
accelerated device's major block device number, the struct uprtab that
is returned has the upt_bmajordev and upt_unit fields set to NODEV.
PRENABLE
The argument to ioctl is a pointer to a dev_t. This enables
Prestoserve caching on the specified file system.
PRDISABLE
The argument to ioctl is a pointer to a dev_t. If all cached data for
the specified file system can be successfully written to disk,
Prestoserve caching is disabled for this file system.
ERRORS
Prestoserve license not registered
This message is displayed if you attempt to use Prestoserve on a system
that has not had its license registered. It is necessary to register a
valid license in order to use Prestoserve.
presto: Block device N currently not present, delay writing of its buffers
During a system reboot, dirty buffers were found for a block device with
the major number N. The dirty buffers could not be written to the device
because the device was not registered with Prestoserve. Prestoserve will
remain in the ERROR state until the device with major number N registers
itself with Prestoserve, at which time the dirty buffers will be flushed
back to the device.
presto: using %d bytes of NVRAM at 0x%x
This message is displayed at boot time and indicates that Prestoserve
recognized its control information portion of the cache. It is a normal
Prestoserve startup message.
presto: initializing %d bytes of NVRAM at 0x%x
This message is displayed at boot time and indicates that Prestoserve did
not recognize the cache as being in either a clean (containing no data) or
a dirty (containing data) state. The message is usually displayed when the
cache is used for the first time, after the cache has been cleared by using
a diagnostic command, or after backup battery failure.
presto: NVRAM tested %s
This message is displayed at boot time, and it indicates that the cache
tested as either "read/write ok" or "readonly ok." The message is a normal
Prestoserve startup message.
presto: %s battery %s
The status for the primary battery or a secondary battery, if applicable,
is reported as either OK , LOW , or DISABLED . This message is displayed at
boot time and when there is a change in the state of the backup battery
power level.
presto: cache contains dirty data
This message is displayed at boot time if Prestoserve was not shut down by
using the normal system shutdown procedures.
presto: %d dirty buffers found
This message indicates that dirty buffers were found after the system
rebooted. The data is written to the intended disks as soon as possible,
usually when the first I/O request occurs for any accelerated device.
presto: writing dirty buffers
This message indicates that Prestoserve has begun to write the data in the
dirty buffers to the intended disks.
presto: dirty buffers written
This message indicates that the data in the dirty buffers has been
successfully written to the intended disks.
presto: using software version %d -- version %d last used
This message is displayed at boot time and indicates that the kernel is now
being run with a version of the Prestoserve software that is different from
the version used previously. Usually, this message is displayed when you
first boot the system after performing a software upgrade.
presto: expected sizes %d, %d -- found %d, %d
This message indicates that the block size and fragment size in the
Prestoserve control information portion of the cache are different from the
information that was expected. This message should only be displayed when
you first boot the system after performing a software upgrade.
presto: NVRAM increased from %d to %d bytes at 0x%x
This message indicates that only a portion of the Prestoserve cache was
being used when the system was shut down, but now Prestoserve is using the
entire cache. The presto -s command, which changes the size of the
Prestoserve cache, is described in presto(8).
presto: decreased from %d to %d bytes!
This message indicates that a hardware or software problem exists because
the size of the Prestoserve cache at reboot is less than the size of the
cache when the system shut down.
presto: dirty buffers found for host id 0x%x,
which is different from this host's id (0x%x)
This message is displayed at boot time and indicates that Prestoserve was
not shut down normally and that the cache contents were previously in a
different system (for example, either the cache was moved or the system ID,
which is usually the on-board Ethernet hardware address, has changed).
Prestoserve allows you to do one of the following interactively: discard
the data, write the data to disk, or halt the machine.
The Prestoserve cache failed memory self-tests.
The cache may contain data which has not been written to disk yet.
When these messages are displayed, Prestoserve allows you to do one of the
following interactively: continue with the boot or halt the machine.
presto: error %d opening dev (%d, %d), skipping writing of its buffers...
This message indicates that dirty Prestoserve buffers were found after the
system rebooted, and the data in the dirty buffers could not be written to
the specified device because the device failed to open. You should verify
that the device is online and that the kernel successfully found the device
at boot time. Refer to errno(2) for a complete description of the error.
presto: error %d opening block device (%d, %d)
This message indicates that the specified device failed to open. You
should check your disk configuration and make sure that the drive is on
line. Refer to errno(2) for a complete description of the error.
presto: error %d ioctl'ing dev (%d, %d)
This message indicates that an ioctl failed for the specified device.
Refer to errno(2) for a complete description of the error.
presto: can NOT do direct I/0 for block device (%d, %d)
presto: using block device (%d, %d) in `bounceio' mode
These messages indicate that the disk controller for the specified device
could not directly address the cache when Prestoserve was enabled on the
file system.
presto: flush dirty buffers
This message is displayed when Prestoserve is in the PRERROR state and
receives a request to write the data in a dirty buffer to the intended
disks.
presto: Block device %d not present or is not Presto-ized in this kernel!
This message indicates that Prestoserve was not shut down cleanly, and the
system was previously running a kernel with an accelerated device that the
current kernel does not accelerate. You should boot a kernel that
accelerates all the devices that were previously accelerated.
presto: NVRAM probe error
This message is displayed at system startup if a Prestoserve cache
read/write error occurred, and it indicates that the cache could not be
accessed. It indicates a hardware or software error.
presto: failed to write and read 0x%x from 0x%x
This message indicates that the Prestoserve cache failed the read/write
test at the specified address.
presto: error on dev (%d, %d)
This message indicates that an I/O error occurred on the specified disk
during a Prestoserve write-back operation.
presto: not enough backup battery power!
This message indicates that there is inadequate backup battery power.
Prestoserve attempts to write all Prestoserve cache data to the intended
disks and then enters the PRERROR state.
presto: disabling...
This message indicates that Prestoserve disabled itself because of
inadequate backup battery power or because a disk error occurred during a
write to disk.
presto: back online!
This message indicates that a disk error or low backup battery power
condition has been corrected and that Prestoserve is enabled again.
Errors
[EACCESS] Indicates that Prestoserve is not registered for use on this
system.
[EPERM] Indicates that a caller whose uid is not root tried to use the
PRSETSTATE, PRSETMEMSZ, PRRESET, PRENABLE or PRDISABLE command.
[EBUSY] Indicates that you tried to use the PRSETSTATE, PRSETMEMSZ, or
PRDISABLE command, but a fatal disk error or a battery problem
exists.
[ENOMEM] Indicates that the memory size you specified in the PRSETSTATE
command exceeds the maximum size of the cache reported in the
presto_status structure.
[ENODEV] Indicates that Prestoserve was not successfully started at boot
time, or it indicates that you used the PRENABLE or PRDISABLE
command and the device specified by dev_t is not a device
initialized for use with Prestoserve or an error occurred in
trying to open/ioctl the device.
[EINVAL] Indicates that an invalid argument was specified with the
PRSETMEMSZ or PRSETSTATE command or that an invalid command was
used.
FILES
/dev/pr0 Generic Prestoserve control device
RELATED INFORMATION
errno(2), ioctl(2), presto(8), dxpresto(8X), prestoctl_svc(8),
prestosetup(8), prestotab(4)
Guide to Prestoserve