Dell PowerVault MD3420 - Manual (Page 120)

performance is maximized when a single I/O request is serviced with a single data stripe; use smaller
values for the segment size. To change the segment size, run the following command:
set virtualDisk ([virtualDiskName] | <wwid>)
segmentSize=segmentSizeValue
where, segmentSizeValue is the new segment size you want to set. Valid segment size values are 8, 16,
32, 64, 128, 256, and 512. You can identify the virtual disk by name or World Wide Identifier (WWID) (see
Set Virtual Disk).
Defragmenting A Disk Group
When you defragment a disk group, you consolidate the free capacity in the disk group into one
contiguous area. Defragmentation does not change the way in which the data is stored on the virtual
disks. As an example, consider a disk group with five virtual disks. If you delete virtual disks 1 and 3, your
disk group is configured in the following manner:
space, virtual disk 2, space, virtual disk 4, virtual disk 5, original unused space
When you defragment this group, the space (free capacity) is consolidated into one contiguous location
after the virtual disks. After being defragmented, the disk group is:
virtual disk 2, virtual disk 4, virtual disk 5, consolidated unused space
To defragment a disk group, run the following command:
start diskGroup [diskGroupNumber] defragment
where, diskGroupNumber is the identifier for the disk group.
NOTE: Defragmenting a disk group starts a long-running operation.
Using SSD Cache
If you are using solid-state disks (SSDs) in your storage array, you can configure SSD cache and model
potential workload throughput improvements, including cache hit percentage and average response
time. SSD cache improves read-only performance by logically grouping SSDs together to provide
secondary cache to the primary cache in the RAID controller module memory.
Enabling SSD Cache For A Virtual Disk
This set virtualDisk command turns SSD caching on or off on a standard virtual disk, snapshot
virtual disk or a consistency group snapshot virtual disk. Set the ssdCacheEnabled parameter to TRUE to
enable SSD caching.
For standard virtual disks:
set virtualDisk ["virtualdiskName"]
ssdCacheEnabled=TRUE
For snapshot virtual disks:
set snapVirtualDisk ["virtualdiskName"]
ssdCacheEnabled=TRUE
For a consistency group snapshot virtual disk:
set cgSnapVirtualDisk ["cgSnapshotVirtualDisk"]
ssdCacheEnabled=TRUE
When you turn off SSD caching for a virtual disk, cache contents is purged. You can turn on SSD caching
for only one virtual disk per command.
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