chvol(8) System Manager's Manual chvol(8)
NAME
chvol - changes the attributes of a volume
SYNOPSIS
/sbin/chvol [-l] [-r blocks] [-w blocks] [-t blocks] [-c on | off] [-A] special domain
OPTIONS
Activates a volume after an incomplete addvol or rmvol operation. Turns I/O consolidation mode on or off. Displays the range of I/O
transfer sizes, in 512-byte blocks, as calculated by the kernel, based on the disk's geometry:
rblks displays the minimum, the maximum, and the preferred transfer size for reads.
wblks displays the minimum, the maximum, and the preferred transfer size for writes. Specifies the maximum number of 512-byte
blocks that the file system reads from the disk at one time. Specifies the maximum number of dirty, 512-byte blocks that the file
system will cache in-memory (per volume in a domain). Dirty means that the data has been written by the application but the file
system has cached it in memory so it has not yet been written to disk.
The number of blocks must be in multiples of 16. The valid range is 0-32768. The default (when a volume is added to a domain) is
16,384 blocks. For optimal performance, specify blocks in multiples of wblks (as specified by the -w option) and multiples of rblks
(as specified by the -r option). Specifies the maximum number of 512-byte blocks that the file system writes to the disk at one
time.
OPERANDS
Specifies the block special device name, such as /dev/disk/dsk2c. Specifies the name of the file domain.
DESCRIPTION
The chvol command enables you to change the attributes of a volume in an active domain. For example, the file system can consolidate a
number of I/O transfers into a single, large I/O transfer. The larger the I/O transfer, the better the file-system performance. If you
attempt to change the attributes of a volume in a domain that is not active, an error message is produced.
The initial I/O transfer parameter for both reads and writes is typically 128 or 256 blocks, depending on the disk driver's preferred I/O
transfer rate. Once you change the I/O transfer parameters with the -r option or the -w option, the parameters remain fixed until you
change them again. The values for the I/O transfer parameters are limited by the device driver. Every device has a minimum and maximum
value for the size of the reads and writes it can handle. If you set a value that is outside of the range that the device driver allows,
the device automatically resets the value to the largest or smallest it can handle.
By default, the I/O consolidation mode (cmode) is on. The cmode must be on for the I/O transfer parameters to take effect. You can use the
-c option to turn the cmode off, which sets the I/O transfer parameter to one page.
Interrupting an rmvol operation can leave the volume in an inaccessible state. If a volume does not allow new allocations after an rmvol
operation, use the chvol command with the -A option to reactivate the volume.
Using the chvol command without any options displays the current cmode and the I/O transfer parameters.
RESTRICTIONS
The values for the wblks and rblks attributes are limited by the device driver.
You must be the root user to use this command.
EXAMPLES
The following example displays the cmode and the I/O transfer parameters of the /dev/disk/dsk1c volume in the domain1 file domain: # chvol
/dev/disk/dsk1c domain1 rblks = 128 wblks = 128 cmode = on thresh = 16,384 The following example additionally toggles the cmode: # chvol
-c off /dev/disk/dsk1c domain1 # chvol /dev/disk/dsk1c domain1 rblks = 128 wblks = 128 cmode = off thresh = 16,384 The following example
continues by changing the I/O transfer parameters of reads (rblks) and writes (wblks) from 128 blocks to 256 blocks. Note that the cmode
is off and must be on before the parameters take effect: # chvol -r 256 -w 256 -c on /dev/disk/dsk1c domain1 chvol /dev/disk/dsk1c domain1
rblks = 256 wblks = 256 cmode = on thresh = 16,384 The following example shows the I/O transfer range on domain1: # chvol -l
/dev/disk/dsk0a domain1 chvol /dev/disk/dsk0a domain1 rblks: min = 16 max = 32768 pref = 256 wblks: min = 16 max = 32768 pref = 256
SEE ALSO
advfs(4), showfdmn(8)
chvol(8)