presto(8) System Manager's Manual presto(8)
NAME
presto - Controls and monitors the Prestoserve file system accelerator
SYNOPSIS
/usr/sbin/presto [options]
OPTIONS
Disables Prestoserve and writes the Prestoserve cache data to the intended disks. If no file systems are specified, all accelerated file
systems are disabled, and the Prestoserve state is set to DOWN.
The filesystem parameter can be used to disable specific file systems. You specify filesystem as a directory mount point (for exam-
ple, /usr). If no file systems are specified, all accelerated file systems are disabled, and the Prestoserve state is set to DOWN.
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.
This option does not reset Prestoserve statistics.
The -d option takes effect before the -u or -R options. Similar to the -d option, 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 Flushes (writes) the Prestoserve cache data to the intended disks, but leaves the cache data intact.
If the option 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 option, the data in the Prestoserve cache remains after it is written to the intended disks. Lists the
accelerated file systems and their mount points in a format similar to the mount command. This option can be used with either NFS
client or server machines. Lists all 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: 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.
Prestoserve acceleration is not enabled on the file system. An error occurred using the file system, and the Prestoserve cache data
has still not been written successfully to the intended disks. Displays Prestoserve information. The information includes the cur-
rent Prestoserve state; the statistics for write, read, and total operations; and battery status. For example: # /usr/sbin/presto
-p dirty = 52, clean = 7, inval = 903, 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 hit on a read represents a physical disk
read that was avoided. 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, the battery state can also be in self test or is charging. Note that if you
use the dxpresto command, batteries that are being self-tested or charged will be displayed as disabled. 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 option, the -R option discards the Prestoserve cache data that could not be written to disk and resets the statistics
information. The option 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 option, because it destroys Prestoserve cache data.
The -R option takes effect before the -u option. 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 option 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 option 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 or smaller than the default minimum size. If you spec-
ify a size that is larger than the default maximum size, the default maximum size is used. If you specify a size that is smaller
than the default minimum size, the default minimum size is used. Sets Prestoserve state to UP, and enables acceleration.
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.
The filesystem parameter can be used to enable specific file systems. You specify filesystem as a directory mount point (for exam-
ple, /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 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. Similar to the -u option, 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
Specifies verbose mode. This option prints extra information to standard output. The information can be used for debugging pur-
poses.
DESCRIPTION
The presto command allows you to accelerate file systems, obtain Prestoserve status, and administer Prestoserve.
If invoked with no options, 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 opera-
tions 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.
FILES
Generic Prestoserve control device.
SEE ALSO
Commands: prestoctl_svc(8), prestosetup(8), dxpresto(8X)
Files: prestotab(4)
Networking: presto(7)
Guide to Prestoserve
presto(8)