presto - Controls and monitors the Prestoserve file system
accelerator
/usr/sbin/presto [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 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 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 = 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 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 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 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 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 purposes.
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 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.
Generic Prestoserve control device.
Commands: prestoctl_svc(8), prestosetup(8), dxpresto(8X)
Files: prestotab(4)
Networking: presto(7)
Guide to Prestoserve
presto(8)
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