presto(8)presto(8)NAMEpresto - 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
example, /usr). If no file systems are specified, all acceler‐
ated file systems are disabled, and the Prestoserve state is set
to DOWN.
Do not specify a block device because some functional subsys‐
tems, 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 suc‐
cessfully to the intended disks. Displays Prestoserve informa‐
tion. The information includes the current Prestoserve state;
the statistics for write, read, and total operations; and bat‐
tery 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 buf‐
fers. 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 com‐
puted 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 sta‐
tistics 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 speci‐
fied 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 specify 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 mini‐
mum size is used. Sets Prestoserve state to UP, and enables
acceleration.
If no file systems are specified, all local writable file sys‐
tems that are mounted will have Prestoserve enabled. File sys‐
tems 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
example, /usr).
Do not specify a block device because some functional subsys‐
tems, 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 pre‐
vious error condition has been corrected. Similar to the -u
option, but sets the Prestoserve state to UP only if the speci‐
fied 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 purposes.
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 bat‐
teries.
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 condi‐
tions 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)