[Novalug] best hard disk setup for home file server?
Bryan J. Smith
b.j.smith at ieee.org
Wed Oct 14 20:14:48 EDT 2009
I'm sorry, but it is very, very much true.
A 2-disc RAID-0+1 (some vendors call it RAID-10) stripes across
50% of two discs, and then mirrors the stripe on each disk to the
other 50% of the other disk. It is fully redundant and allows for
just as good of read performance when operations are high more
single threaded. During writes, two passes must be made to each
A 4-disc RAID-0+1 (typically called RAID-10) allows for two, independent
read operations from each mirror of the original, 2-disc striped. It also
only requires one pass to be made to each disc during writes.
Several SAS host adapters do a 2-disc RAID-10, and newer, intelligent
controllers allow it. Linux's MD is very much capable of it as well, and it
is fully redundant. It will just not be as high as performing at a 4-disc at
multiple read operations or any write.
In fact, a 3-disc RAID-0+1 where it is striped across the 50% of three
disks, mirrored to the other 50% of each, could have higher, sequential
read DTRs than a traditional, 4-disc RAID-0+1 where you have whole
I know these concepts confuse many people, but to get fully redundant
mirroring with added performance of striping, only two (2) discs are
actually required. But it is not ideal for write performance as two commits
must occur to each disc for each block written instead of only one as in
the case of 4-disc RAID-0+1.
----- Original Message ----
From: Aaron Porter <atporter at gmail.com>
That's not (really) true. For RAID10 you need 4 block devices (could
be all on one disk, but seriously...) -- RAID10 is STRIPED and
MIRRORED, so you need at least 2 devices to MIRROR and at least 2
MIRRORS to STRIPE. A 3 legged monstrosity could be some ugly
combination of a RAID1 + RAID0 or A RAID0 + RAID1, but would not
really be striped & mirrored.
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