Re: RAID5 slowness (how to fix?)

David Stuart wrote:
We are
currently backing up over the network to another machine

What kind of network and what kind of backup software are you using?

Over 100 Mbit/sec Ethernet you'll likely only get 10 MByte/sec performance. Transferring the 600 GB of data that your array could hold could take nearly 17 hours by my math.

Over gigabit Ethernet, you'll max out at 100 MBytes/sec (but only if you've got powerful hardware on both ends) if you're transferring everything.

Better backup software that only transfers what is necessary (such as rsync or an incremental backup) will lower the network overhead, obviously.

hdparm -tT yields the following:

# hdparm -tT /dev/md0

/dev/md0:
Timing buffer-cache reads: 1764 MB in 2.00 seconds = 882.00 MB/sec
Timing buffered disk reads: 18 MB in 3.23 seconds = 5.57 MB/sec

That's awfully slow indeed. So the network isn't the only problem. You definately need each drive to be master on its own IDE channel.
.

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