Hi all!
I've been running raid-0 and linear modes on a disk array for some time. This
works really well! (I guess you allready knew :)
Now, I moved the disks (six quantum fireball 6 GB scsi on two ncr53c810 controllers,
three disks on each), into another machine and wanted to run RAID-5 on them.
The kernel which worked so well for me was 2.0.35 with md-tools 0.35.
The new machine runs 2.1.125, and I use the raid-5 capabilities in that kernel
unpatched. Furthermore, I use raidtools-0.41.
I followed the instructions, and got a raid-5 array up running, or ``crawling''...
mke2fs takes long time (I went away from the machine, so I don't have timings).
Large writes almost hangs the machine. A ckraid takes 80 minutes. Bonnie on the
array gave theese weird timings:
-------Sequential Output-------- ---Sequential Input-- --Random--
-Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
Machine MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU /sec %CPU
400 5286 92.3 107 16.8 3557 18.7 3104 48.9 11332 19.9 387.1 7.4
What really pussles me is, that putc() seems to give good results, while block writes
are unbelievably slow. I'm aware that raid-5 will always be slower than raid-0, but
this is extreme.
For reference, I tried setting up the array as raid-0 again. This time the machine
stayed responsive, and behaved much like the old setup used to. Bonnie here gives:
-------Sequential Output-------- ---Sequential Input-- --Random--
-Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
Machine MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU /sec %CPU
400 5403 84.3 18576 35.6 6859 25.5 4787 74.3 15879 26.6 398.8 6.4
What is wrong ? Is raid-5 really so inherently slow, and has to lock the machine,
or am I missing something ? (The machine is a dual PII-350, I guess it should be
able to calculate the parity fast enough)
Furthermore, where can I get recent information about the raid tools ? I looked at
some sites, but often they have missing links or ``last modified early 1997'' in them.
Thank you very much.
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:.........................: putrid forms of man :
: Jakob Østergaard : See him rise and claim the earth, :
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