Dell PowerVault ME4 Series Storage System CLI Guide

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set volume-cache-parameters


Description	Sets cache options for a specified volume or specified volumes. 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. CAUTION:Changing the cache optimization setting while I/O is active can cause data corruption or loss. Before changing this setting, quiesce I/O from all initiators.
Minimum role	manage
Syntax	set volume-cache-parameters [optimization standard\|no-mirror] [read-ahead-size disabled\|adaptive\|stripe\|512KB\|1MB\|2MB\|4MB\|8MB\|16MB\|32MB] [write-policy write-back\|write-through\|wb\|wt] `volume` \|all
Parameters	[optimization standard\|no-mirror] Optional. Sets the cache optimization mode: standard: This controller cache mode of operation is optimized for sequential and random I/O and is the optimization of choice for most workloads. In this mode, the cache is kept coherent with the partner controller. This mode gives you high performance and high redundancy. This is the default. no-mirror: In this mode of operation, the controller cache performs the same as the standard mode with the exception that the cache metadata is not mirrored to the partner. While this improves the response time of write I/O, it comes at the cost of redundancy. If this option is used, the user can expect higher write performance but is exposed to data loss if a controller fails. [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 (increasing LBAs) or reverse (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 NRAID and RAID-1 disk groups 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. [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 advanced-settings command. `volume` The name or serial number of the volume to change. A name that includes a space must be enclosed in double quotes. `volume` \|all Specifies either: The name or serial number of the volume to change. A name that includes a space must be enclosed in double quotes. all: Apply the changes to all volumes.
Examples	Set the cache policy, optimization mode, and read-ahead size for volume V1. # set volume-cache-parameters write-policy wb optimization standard read-ahead-size stripe V1
See also	show cache-parameters show volumes