HP MSA 1040 HP MSA 1040 CLI Reference Guide (762782-001, March 2014) - Page 141

set cache-parameters Description Sets a volume's cache options. Settings you can change include: NOTE: Only change the read-ahead cache settings if you fully understand how the host operating system, application, and adapter move data so that you can adjust the settings accordingly. Be prepared to monitor system performance and adjust read-ahead size until you find the optimal size for your application. Syntax set cache-parameters [write-policy write-back|write-through|wb|wt] [optimization standard|no-mirror|atomic-write] [read-ahead-size disabled|adaptive|stripe|512KB|1MB|2MB|4MB|8MB|16MB|32MB] volume Parameters write-policy write-back|write-through|wb|wt Optional. Sets the cache write policy, which determines when cached data is written to the disks. The ability to hold data in cache while it is being written to disk can increase storage device speed during sequential reads. • write-back or wb: Write-back caching does not wait for data to be completely written to disk before signaling the host that the write is complete. This is the preferred setting for a fault-tolerant environment because it improves the performance of write operations and throughput. This is the default. • write-through or wt: Write-through caching significantly impacts performance by waiting for data to be completely written to disk before signaling the host that the write is complete. Use this setting only when operating in an environment with low or no fault tolerance. You can configure the write policy to automatically change from write-back to write-through when certain environmental events occur, such as a fan failure. For details, see help for the set auto-write-through-trigger command. optimization standard|no-mirror|atomic-write Optional. Sets the cache optimization mode: • standard: Optimizes cache for both sequential and random reads. This is the default. • no-mirror: When this mode is enabled, each controller stops mirroring its cache metadata to the partner controller. This improves write I/O response time but at the risk of losing data during a failover. ULP behavior is not affected, with the exception that during failover any write data in cache will be lost. • atomic-write: Not supported. read-ahead-size disabled|adaptive|stripe|512KB|1MB|2MB|4MB|8MB|16MB |32MB Optional. Controls the use and size of read-ahead cache. You can optimize a volume for sequential reads or streaming data by changing the amount of data read in advance. Read ahead is triggered by sequential accesses to consecutive logical block address (LBA) ranges. Read ahead can be forward (that is, increasing LBAs) or reverse (that is, decreasing LBAs). Increasing the read-ahead size can greatly improve performance for multiple sequential read streams. However, increasing read-ahead size will likely decrease random read performance. • disabled: Disables read ahead. • adaptive: Enables adaptive read-ahead, which allows the controller to dynamically calculate the optimum read-ahead size for the current workload. This is the default. • stripe: Sets the read-ahead size to one stripe. The controllers treat non-RAID and RAID-1 vdisks internally as if they have a stripe size of 512 KB, even though they are not striped. • 512KB, 1MB, 2MB, 4MB, 8MB, 16MB, or 32MB: Sets a specific read-ahead size. set cache-parameters 141