Well, it’s been a week now since I setup the 4-disk RAID5 array using 16kb stripe size and writing with 64kb truecrypt cluster sizes. While the read performance was good, write performance was absolutely dismal.
I somewhat expected writes to be slow because of the parity calculations during RAID5 write operations, but the actual performance was far worse than I’m willing to tolerate. On a 2GB file, writes would start out at 40MB/s and then slow to a paltry 20MB/s after a minute or so. That was even after some setting improvements, because when I had a sub-optimal stripe size and cluster size combination, the same file would transfer at only 12MB/s. I would actually be OK with 20MB/s, but I found out that if I queued up a large amount of files to be written at once, it would cause the controller to crash after 50GB or so. TERRIBLE!
To top it off, I had some physical connection problems where gravity was pulling on a power cable and eventually yanked one out, causing the drive to be marked for a rebuild. The Silicon Image software has a really crappy java interface and didn’t allow me to rebuild the array, I’m so totally fed up with it. Good thing I didn’t delete the data after transferring it, I was able to just delete the array and start over without worries.
So, now I am using RAID10 and I’m much happier about it. Read operations of a 1GB file from the array to my RAMDisk occur at a zippy 80MB/s, write operations are sustaining 47MB/s, and to top it all off I can sustain two disk failures without losing data. (actually, definitely at least one failure, the second failure would have a 1/3 chance of causing me to lose data. but that’s still way better than the single disk of fault-tolerance with RAID5) There is the disadvantage of only having 596GB of usable space instead of 894GB, but for the huge performance and reliability bonus I now believe it’s worth it.
I don’t think I’m going to use RAID5 anymore unless it’s on an expensive hardware-RAID controller with good array management software. I’m thinking that Promise, Intel branded would be ok. And even then, I would still rather use RAID10 if drive cost wasn’t an issue.
For more about RAID 10, visit acnc