[clue-tech] Software RAID

[Jeff Schroeder]

Russ asked:

> At any rate, what difference does
> it make to read a swap from a physical device, rather than two
> physical devices?  Since this is a mirror, we're reading the same
> information from both drives at the exact same time.  So there
> shouldn't be a significant time savings by having swap on a physical
> drive, compared to the RAID.

I'm not a RAID expert, but I don't think you want swap on RAID.  You're 
right in that reading from the RAID won't make much difference, since 
the data is the same on both physical devices.  However, when you're 
writing to swap, the system has to write to both devices.  Thus your 
swap writes take at least 2x longer.  Swap is slow enough as it is. ;)

What you should probably do instead is specify *two* swap partitions in 
your /etc/fstab file.  Just give the physical devices.  That'll not 
only improve your swap performance, but will help you if a drive fails 
because you won't need to switch things (I think).

See the software RAID HOWTO for more info:

http://www.tldp.org/HOWTO/Software-RAID-HOWTO-2.html#ss2.3

HTH,
Jeff