Janek Kozicki wrote:
Hello,
My three HHDs have following speeds:
hda - speed 70 MB/sec
hdc - speed 27 MB/sec
sda - speed 60 MB/sec
They create a raid1 /dev/md0 and raid5 /dev/md1 arrays. I wanted to
ask if mdadm is trying to pick the fastest HDD during operation?
Maybe I can "tell" which HDD is preferred?
If you are doing raid-1 between hdc and some faster drive, you could try
using write-mostly and see go that works for you. For raid-5, it's
faster to read the data off the slow drive than reconstruct it with
multiple reads to multiple othjer faster drives.
This came to my mind when I saw this:
# mdadm --query --detail /dev/md1 | grep Prefer
Preferred Minor : 1
And also in the manual:
-W, --write-mostly [...] "can be useful if mirroring over a slow link."
many thanks for all your help!
I have two thoughts on this:
1 - if performance is critical, replace the slow drive
2 - for most things you do, I would expect seek to be more important
than transfer rate
--
bill davidsen <davidsen@xxxxxxx>
CTO TMR Associates, Inc
Doing interesting things with small computers since 1979
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