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Re: Promise RAID-1 vs software RAID-1



Jack Howarth wrote:
    I have a couple questions about the finer details of
the Promise RAID-1 vs the use of software RAID-1 with
the promise-sata driver. We have two machines here, one
of which has RedHat 9 and the Promise RAID driver installed
for a RAID-1 mirror. The second machine has Fedora Core 2
with the promise-sata driver used for a software RAID-1
mirror. The question has to do with any speed improvements
that the Promise RAID-1 might have on reads. One of our
users has been told that the Promise RAID-1 actually reads
off of both drives at the same time to achieve a speed
increase on reads (by splitting the reads). Is this true
and if so does the software RAID-1 attempt something like
this? I suspect this isn't the case and they are confusing
RAID-1 with RAID 0+1. My understanding was that a RAID 0+1
required 4 drives and wasn't possible with just two drives.
    If it is true that the Promise RAID 1 does in fact
read partially from each drive to increase the throughput,
does software RAID-1 do the same?

Don't know about the Promise software raid driver but the Linux kernel does give you the ability to do simultaneous reads from both drives in a Linux RAID 1 mirror pair.




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