Ah, it's something to with RAID1 drives having to skip blocks that are
read from the other drives, right?
i.e., it's about the head having to move further, instead of to just the
next block? I suppose that's only important for sequential reads, and it
would be 'fixed' to some extent by the drives' cache...
Max.
Max Waterman wrote:
Hi,
I've been reading a bit about RAID 1 vs RAID 0 on these pages :
<http://www.pcguide.com/ref/hdd/perf/raid/levels/single_Level1.htm>
They seem to suggest RAID 0 is faster for reading than RAID 1, and I
can't figure out why.
Clearly, the write performance is worse for RAID 1 than RAID 0 since
with RAID 1 that data you are writing at the same time is the same for
both drives; but for reading, why can't the two drives be read as if
they were a stripe.
You could even read the stripe in any 'direction'...when the RAID 1
array has more than two disks, that would make RAID 1 *faster* than RAID 0.
ie
RAID 0
file is like this
0 1 2 3 4
can only be read in that order :
0 1 2 3 4 but
RAID 1
file is like this
A B C D E
---------
0 0 0 0 0
1 1 1 1 1
2 2 2 2 2
3 3 3 3 3
4 4 4 4 4
can be read as
A B C D E
0
1
2
3
4
or
1
0
3
4
2
or whatever...
Could it not help with small files and when not streaming?
Am I missing something?
Max.
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