Re: doesm mdadm try to use fastest HDD ?
Bill Davidsen <[EMAIL PROTECTED]> writes: > 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. Won't it naturally balance reads according to the disk speeds if there are enough streams reading? I know raid1 prefers a disk that is already near the location it wants. But won't it pick the first idle one if there is no disk near the location? And the faster disk will be idle more often. MfG Goswin - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: doesm mdadm try to use fastest HDD ?
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 <[EMAIL PROTECTED]> CTO TMR Associates, Inc Doing interesting things with small computers since 1979 - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
doesm mdadm try to use fastest HDD ?
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? 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! -- Janek Kozicki | - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
