what about mirroring only ? raid 1 ?
I always thought that raid 1 is the fastest, am I true ?
I don't really need more then 3GB data and I have two 36GB HD. so I don't
need lvl 0 nor lvl 5 unless raid 1 is slower.
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----- Original Message -----
From: "Markus Wollny" <Markus.Wollny@computec.de>
To: <holger@marzen.de>
Cc: <pgsql-general@postgresql.org>
Sent: Tuesday, October 21, 2003 11:00 AM
Subject: Re: [GENERAL] Recomended FS
> Theory vs. real life. In Theory, RAID5 is faster because less
> data have
> to be written to disk. But it's true, many RAID5 controllers
> don't have
> enough CPU power.
I think it might not be just CPU-power of the controller. For RAID0+1
you just have two disc-I/O per write-access: writing to the original set
and the mirror-set. For RAID5 you have three additional
disc-I/O-processes: 1. Read the original data block, 2. read the parity
block (and calculate the new parity block, which is not a disk I/O), 3.
write the updated data block and 4. write the updated parity block. Thus
recommendations by IBM for DB/2 and several Oracle-consultants state
that RAID5 is the best compromise for storage vs. transaction speed, but
if your main concern is the latter, you're always best of with RAID0+1;
RAID0+1 does indeed always and reproducably have better write
performance that RAID0+1 and read-performance is almost always also
slightly better.
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