Re: Poor raid 1 performance?

Peter wrote:

>> I've been following this here a bit, and I also don't understand why
>> RAID1 can't provide the same increase in speed as RAID0. With RAID0,
>> you have the data in stripes over several disks. With RAID1, you have
>> all the data over several disks, which should make it possible to read
>> a RAID1 array similarly to a RAID0 array (that is, the controller could
>> just read the data arbitrarily from each of the two disks, and could,
>> so to speak, "virtually stripe" them for reading).
>
> Maybe, because how data is organized on each disk, it makes difficult to
> stream (read sequentially) with full speed, while reading every other
> sector?

I'm not sure, but I don't think the data is organized much differently. The
two disks of a RAID1 (2 disk) array are supposed to have identical data. So
what hinders a RAID1 controller to read one stripe from disk A while
reading another stripe from disk B (just like the same controller would do
in a RAID0 configuration)? It also could do head movement optimization,
like using one disk for reading the disk index and the other disk for
reading the data (or more elaborate schemes to minimize head movement).
>From what people wrote here, the RAID controllers don't seem to do this
with RAID1. Anybody knows why not?

Gerhard
.

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