[lug] raid

[Peter Hutnick]

D. Stimits said:

> There is no technical reason to stop you, it'll work fine, but having
> slightly different specs can result in far less optimum throughput than
> with matched disks.

This is 100% correct.

> But for raid 5, those in series can be matched, and
> the one doing checksum would be nice as the 15krpm disk (till you lose a
>  drive).

This is nonsense.  RAID 5 does not use an independent "checksum" (parity)
disk.  It alternates, like:

Disk1  Disk2  Disk3
data   data   parity
parity data   data
data   parity data
.. . .

> You could use the 10k for separate swap, plus other things,
> like  /tmp/, and gain other benefits. Raid 5 of course is not for
> performance  reasons anyway, it is for the case of disk failure, so you
> will probably  be reasonably happy with it.

This all makes sense, and is good advice if you use RAID-/4/, not 5.  See
http://www.tldp.org/HOWTO/Software-RAID-HOWTO-2.html.

-Peter