SVM did RAID 0+1 i.e. mirrored entire sub-mirrors. However SVM
mirroring did not incur the problem that Richard alludes to, i.e. a
single disk failure on a sub-mirror did not take down the entire
sub-mirror, because the reads and writes are smart and acted as though
it was a RAID 1+0. Thus as long as there was one valid copy of data
available, reads and writes would be satisfied.
-Sanjay
Dennis Clarke wrote:
Dennis Clarke wrote:
While ZFS may do a similar thing *I don't know* if there is a published
document yet that shows conclusively that ZFS will survive multiple disk
failures.
?? why not? Perhaps this is just too simple and therefore doesn't get
explained well.
That is not what I wrote.
Once again, for the sake of clarity, I don't know if there is a published
document, anywhere, that shows by way of a concise experiment, that ZFS will
actually perform RAID 1+0 and survive multiple disk failures gracefully.
I do not see why it would not. But there is no conclusive proof that it will.
Note that SVM (nee Solstice Disksuite) did not always do RAID-1+0, for
many years it would do RAID-0+1. However, the data availability for
RAID-1+0 is better than for an equivalent sized RAID-0+1, so it is just
as well that ZFS does stripes of mirrors.
-- richard
My understanding is that SVM will do stripes of mirrors if all of the disk
or stripe components have the same geometry. This has been documented, well
described and laid out bare for years. One may easily create two identical
stripes and then mirror them. Then pull out multiple disks on both sides of
the mirror and life goes on. So long as one does not remove identical
mirror components on both sides at the same time. Common sense really.
Anyways, the point is that SVM does do RAID 1+0 and has for years.
ZFS probably does the same thing but it adds in a boatload of new features
that leaves SVM lightyears behind.
Dennis
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