Weird RAID 1 performance

Andrei Badea <andrei.badea@xxxxxxxxx> · Sat, 18 Sep 2004 23:11:44 +0200

Hello,

I have a RAID 1 whose write performance I tested by writing a 10 GB file 
to it:

dd if=/dev/zero of=/mnt/data/zeros bs=1024 count=...

Looking at GKrellM I noticed the CPU usage is very jumpy, going from a 
few to 99 percent (but usually is roughly rovers around 50 percent). 
Moreover, the transfer regularly stops for a few seconds (the CPU usage 
is then about 2 percent). The average data transfer rate was 16 MB/s, 
while the disks alone can make almost 25 MB/s.

Is this normal behavior? Can the write performance be tuned (to be less 
"jumpy")?

The reason I'm asking is that I'm encoutering hangs when video capturing 
to this RAID using mencoder and huffyuv. I'm not experiencing the hangs 
when capturing to another partition (not RAID). Neither did I experience 
 hangs during the dd copy.

Maybe the RAID 1 is just not suited for video capture?

The filesystem is ext3 and /etc/raidtab is:

raiddev /dev/md0
        raid-level              1
        nr-raid-disks           2
        nr-spare-disks          0
        persistent-superblock   1
        device                  /dev/hde1
        raid-disk               0
        device                  /dev/hdg1
        raid-disk               1

Thank you for help.

Andrei

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