I understand the fundamental workings of EVA, and I also understand that this so called "Protection Level" is not really a protection level, the VRAID level is this.
However I have double protection set at the moment on 8 1TB FATA disks. I really need some more space and am having a hard time justifying the purchase of new disks, when I can adjust the protection level to single and free up 2TB in a single hit...
Can someone explain what the technical difference is...
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Protection level influences availability The protection level defines the number of disk failureâauto reconstruction cycles that the array can accomplish without replacement of a failed disk. Following a disk failure, the controller re-creates the missing data from the parity information. The data is still available after the disk failure, but it is not protected from another disk failure until the reconstruction operation completes. For example, âsingleâ protection level provides continued operation in the event of 2 disk failures, assuming the reconstruction of the first failed disk completes before the second and so on till the number of the failed disk of 4 in the double disk protection.
None disk protection
For Vraid1 and Vraid5, protection level ânoneâ provides resilience to a single disk failure; whereas Vraid6 provides resilience to a dual disk failure; however, this is not a best practice configuration. Vraid0 offers no protection from a disk failure.
Right, the so-called "protection level" has nothing to do with RAID redundancy - that is provided by the VRAID-level: 1, 5, 6.
The EVA's virtualization DOES NOT add redundancy (some people I've talked to really believed this!). VRAID-0 does not provide protection against a disk drive failure.
Think of the "protection level" as some kind of "virtualized set of spare disks". The capacity is 'striped' across all disk drives in a disk group.
Level 0/none does not reserve any capacity.
Level 1/single reserves 2 times the size of the largest disk drive in the disk group.
Level 2/double reserves 4 times. I'm sure by now you understand that it just reserves more space for recovering redundancy, but it does not make your data "more safe". That level is really intended for systems which are not closely monitored and/or replacement parts do not come by quick (in my opinion).
2/4 times is due to the way the EVA stores VRAID-1 redundant information. It does always apply, even if you don't use VRAID-1 - but the EVA must care, because you could change your mind one day and completely fill a disk group with VRAID-1 vdisks.
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