On 03/05/2011 23:34, Keld Jørn Simonsen wrote:
On Tue, May 03, 2011 at 04:52:07PM -0300, Roberto Spadim wrote:
2011/5/3 Morad, Steve<morad@xxxxxxxxxx>:
I have a few questions about volume mirroring performance
implications.
2. Similarly, would a RAID10 configuration give me the same (or
better) read behavior across these same disks, while providing
twice the storage capacity of the above configuration?
RAID10 and RAID1 gives the same storage capacity with the same
disks.
Perhaps he meant a 4-drive RAID1 set? That way reads for any data can
be taken for any drive.
Linux MD RAID10 is actually just another way of doing raid1-like
layouts.
in md world raid1+ raid0 != raid10
raid10 can use layouts raid1 can?t
raid10 have diferent read_balance algorithms than raid1 raid10 with
far layout is better optimized for sequencial read (it?s like raid0
stripe) raid10 with near/offset layoute are better optimized for
multthread
Hmm, raid10 near, offset and far are about the same for multithread,
according to several benchmarks. Actually the far layout has
significant better random read performance than the near layout in
some thests, about 25 % better speed, and about 100 % bettter speed
than raid1.
raid10,far is better for sequential reads - it gives better-than-raid0
performance on average since it will do striped reads from the faster
outer tracks. And for multi-threaded reads, it should also be a little
faster than other raid10 layouts (and raid1, which is much the same as
raid10,near). Since it prefers to get the data from the outer half, you
get the benefits of short-stroking your disks - faster transfer speeds
and less head movement.
The cost of raid10,far is greater head movement for writes - but that is
not the OP's main concern.
If I interpreted correctly that the OP is considering a 4-way mirror,
then perhaps raid10,f4 is ideal - sequential reads will be taken from
all drives at once (in the outer quarter of the disks), and for
multi-thread reads all requested data can be found on any of the disks.
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