RAID5... wow

[poptones]

I've had a raid5 for my main data storage for a while now (and it's already paid off as I had a disc fail and replaced it under warranty... boy, it's nice to not lose data!)

Now that I have my system pretty well reconfigured I decided to experiment with a raid5 "userland." When I build a system I put all user level partitions on /usr - /usr/home, /usr/var, /usr/tmp etc.

Anyway, I decided to see how that compares with a RAID5 version of the same space, so I set up equal sized partitions across the other two discs (that weren't being used for /usr), created a degraded raid5, copied the data over from my active /usr partition and rebooted. Once I was sure it was working ok I just added the old /usr partition into the missing spot on the raid5 and in a few minutes I had a fully functional raid5 for my userland.

I then compared the performance of the (completely software) raid5 to the performance of a single, unencrypted, partition (in this case, root).



Command line used: iozone /oddworld/test
Output is in Kbytes/sec
Time Resolution = 0.000003 seconds.
Processor cache size set to 1024 Kbytes.
Processor cache line size set to 32 bytes.
File stride size set to 17 * record size.
random random bkwd record stride
KB reclen write rewrite read reread read write read rewrite read fwrite frewrite fread freread
512 4 6505 6889 516696 530518 535562 6748 473675 6798 464599 6621 6939 490372 506984

Command line used: iozone /test
Output is in Kbytes/sec
Time Resolution = 0.000003 seconds.
Processor cache size set to 1024 Kbytes.
Processor cache line size set to 32 bytes.
File stride size set to 17 * record size.
random random bkwd record stride
KB reclen write rewrite read reread read write read rewrite read fwrite frewrite fread freread
512 4 6354 6926 516643 526740 623560 6446 463772 6703 465858 6616 6928 483455 512979


Note the performance is roughly equal in spite of "oddworld" being an encrypted software based RAID5.

[Ride Jib]

That's pretty cool. Could you post up links to the information you used to accomplish this? Or if you did it off your own brain-power, could you share some of that knowledge with us?

Thanks

[poptones]

I suppose I could. I only posted that because there is a widespread misconception that "software raids" are somehow not as good as "hardare raids" (even though they are pretty much the same thing until you get to vey high end controllers) and that encryption slows things down in unacceptable fashion.

In this case, write performance is significantly faster on a vanilla partition, but read performance is pretty much equal and the benefits (security, reliability) are significant.