The HP 3PAR Operating System has a logical volume manager that handles volume abstraction at the Virtual Volume layer and also handles sparing. This logical volume manager reserves a certain number of chunklets as spare chunklets depending on the sparing algorithm and system configuration. Unlike many competitive arrays that reserve dedicated spare drives that then sit idle, system-wide sparing with HP 3PAR StoreServ Storage means that spare chunklets are distributed across all drives. This provides additional protection and enables a balanced load that extends the SSD lifespan by providing even wearing. It also protects against performance degradation by enabling a “many-to-many” rebuild in the event of a failure. After the jump I have listed a few CLI commands to check the system-wide sparing algorithm in use and how to change it.
1.showpd -c -p -devtype “disk type (example FC, SSD, NL)”
a.Displays all of the disks of the selected type and shows what each chunklet is doing. Look for the “Free” column under the Spare Chunklets section. This tells you the amount of chunklets being dedicated for sparing on each disk.
a.Displays the sparing algorithm currently in use. In this case the Default setting is selected.
3.setsys SparingAlgorithm “setting”
a.Sets the sparing algorithm. You have 3 options to choose from.
i.Minimal: 1x biggest disk size worth of chunklets per 24 drives with no minimum
ii.Default: 1x biggest disk size worth of chunklets per 24 drives with an enforced 2 disk minimum
iii.Maximal: 1x biggest disk size worth of chunklets per installed type per enclosure