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chvol(8) System Manager's Manual chvol(8) NAME chvol - changes the attributes of a volume SYNOPSIS /sbin/chvol [-r blocks] [-w blocks] [-t blocks] [-c on | off] [-A] spe- cial domain Specifies the block special device name, such as /dev/rz2c. Specifies the name of the file domain. FLAGS 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 768 blocks. For optimal performance, specify blocks in multiples of wblks (as specified by the -w option). Specifies the maximum number of 512-byte blocks that the file system writes to the disk at one time. Turns I/O consolidation mode on or off. Ac- tivates a volume after an incomplete rmvol operation. 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 num- ber 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 messages is produced. The initial I/O transfer parameter for both reads and writes is 128 blocks. Once you change the I/O transfer parameters with the -r flag or the -w flag, the parameters remain fixed until you change them. The values for the I/O transfer parameters are limited by the device dri- ver. 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 re- sets 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 flag to turn the cmode off, which sets the I/O transfer parameter to one page. For file system workloads that are heavily biased toward random writes, use the -t flag to increase the file system's dirty threshold. This may improve file write performance. Interrupting an rmvol operation can leave the volume in an inaccessible state. If a volume does not allow new allocations after an rmvol opera- tion, use the chvol command with the -A flag to reactivate the volume. Using the chvol command without any flags 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 parame- ters of the /dev/rz1c volume in the domain1 file domain: # chvol /dev/rz1c domain1 rblks = 128 wblks = 128 cmode = on The example also toggles the cmode: # chvol -c off /dev/rz1c domain1 # chvol /dev/rz1c domain1 rblks = 128 wblks = 128 cmode = off The 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/rz1c domain1 # chvol /dev/rz1c domain1 rblks = 256 wblks = 256 cmode = on RELATED INFORMATION advfs(4), showfdmn(8) delim off chvol(8)