Software RAID using Linux

An interesting story on how Cornell University built four 2GB Linux NAS using many IDE drives and software RAID:

I finally got my SATA RAID(1) setup going. This is with an Adaptec 1210SA SATA controller and two 200 GB drives.

To handle the heat issues caused by having 4 drives (1 SCSI, 1 IDE, 2 SATA) stacked on each other, I came up with a brilliant idea. (Well, at least I think so!) My previous server (AMD 500, AT board, etc) isn't being used for anything other then to power my FireCard firewall, which only uses the PCI bus for power. So, I yanked the floppy and hard drive from that, and put my two new 200 GB SATA drives in it. Since the SATA cables are thing but long (3+ feet), I feed it from the drives, out through an missing PCI slot cover, into a similarly missing slot on the main server, and to the SATA Controller there.

So essentially I have an external drive enclosure now, with it's own cooling and power.... but it looks like a siamese twin

It doesn't seem like the hardware RAID is going to work under Linux. I first tried a Linux IDE driver for Adaptec 1210SA, but it whined and complained and hung, and saw the drives as separate devices. Eventually I discovered a newer SATA/SCSI driver for the Silicon Image card, which is working quite well. It sees the drives as separate devices and not as a single SCSI drive, but it seems to work really well. Both drives are essentially very new and experimental yet, and require the latest 2.6.2 kernel to work correctly.

Performance is pretty good, too...

Some basic throughput tests using zcav: - 18GB SCSI X15: average 3.9 seconds to seq read 100MB - 60GB ATA100: average 6.7 seconds to seq read 100MB - 200 GB SATA (non-RAID): average 1.7 seconds to seq read 100MB

Not sure what access times are like yet; I'm running some bonnie++ tests on that now.

I just discovered this benchmarking tool...

" It is quite easy to imagine scenarios where you can store some data on the past part of a slow hard drive for better performance than the slow part of a fast hard drive!"

Interesting thought... could make a lot of sense to utilize the faster parts of a slightly older drive for swap or a temporary file place...


See also Hardware, Linux, BackupSystems