Reply to post: by default

HPE's Australian tax failures may have been user error

Nate Amsden Silver badge

by default

3PAR systems will protect against an entire shelf failing(they call it "cage level availability") but it does restrict what types of RAID you can use. e.g. if you have only 2 shelves of disks you can only use RAID 10, not RAID 5 or RAID 6. If you have 8 shelves you could use RAID 6+2 if you really wanted RAID 6. If you wanted RAID 5 the minimum would be 3 shelves for RAID 5 2+1). There are also minimum numbers of disks required on each shelf as well as minimum numbers required for adding to shelves(e.g. if you have a 4 shelf 3PAR system and you want to add more disks/SSDs the minimum SSDs you can add is 8).

Otherwise the admin of the array can change the default behavior to not protect against a shelf failing (3PAR calls it 'magazine level availability', although the concept of magazines is no longer in the Gen5 8k/20k hardware systems they kept the term for now). Though changing this behavior has no effect on minimum numbers of drives per shelf or minimums on upgrades per shelf.

You can also customize having some volumes cage level availability and others magazine level, just like you can have some volumes on RAID 5,some on RAID 6, some on RAID 10, all while sharing the same spindles/SSDs (or you can isolate workloads on different spindles/SSDs if you prefer, and you can of course move stuff around between any tier or media type without app impact).

Back in the early days of 3PAR for eval systems they would encourage the customer to unplug a shelf, or yank a live controller to demonstrate the resiliency(provided it was configured for default/best practice of cage level availability).

In the 11 years I have had 3PAR I have yet to have a shelf fail, though I do stick to cage level availability for all data wherever possible. The only time I have moved a 3PAR array was at a data center that had weight restrictions per cabinet, so we had installed steel plates to distribute the weight more, and needed to get the array up on the plates. My 3PAR SE+ 1 or 2 other professional services people at the time came on site, we shut the system down, removed all of the drive magazines, and moved the cabinets up onto the steel plated platform and re-inserted everything, re cabled everything and turned it back on. Those 3PAR systems could get up to be 2,000 pounds per rack fully loaded, and I think the data center had a limit of 800 pounds per cabinet or something(in a highrise 10+ floors up).

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