[mythtv-users] Linux software raid question

Ian Clark mrrooster at gmail.com
Thu Jun 5 15:33:41 UTC 2008

2008/6/5 Gerald Brandt <gbr at majentis.com>:

> I've been running a 5x250 software raid5 array for a few years.  It's easy
> to setup and maintain and uses very little CPU.  If I had the cash, I'd prob
> convert to hardware raid5, and buy 2 controllers (1 spare).
> Sadly, I don't have the cash, so my biggest decision now is: when I build a
> new system, do I go software raid 5 or software raid 6?

If cash is an issue then you need to look at how likely you are to have more
than 1 drive fail at any given time. How many failures have you had in the
last few years?

How many drives are you planing on RAIDing? The more drives the more likely
to fail. How important is the data? How regular do you backup? (EG, I have a
RAID 5 array, that I can't afford to backup, so I'm more reliant on the
redundancy as I really don't want to loose data.)

If you're building a box just for storage Suns ZFS looks really good, and it
does solve some of the problems in software that you would otherwise need a
hardware RAID card for (or much reduced performance). It's also easy to
admin and fairly scalable.

However, this does mean a move to Solaris (or Nexenta; which is GNU based),
and learning a new (similar) system isn't everyone's idea of fun.

Aside: As there seem to be a lot of linux RAID experts round here, how
critical is the number of discs in a linux RAID 5 array? I've got a 4 disc
RAID 5 array on NetBSD, but I suffer from performance issues (as the number
of discs is not a power of two + 1), but I'm wondering if linux is more
flexible in this regard. (NetBSDs FFS needs a block size that's a multiple
of 2, so tuning stripe size and block size to ensure a full stripe write
whenever possible is not possible with 4 discs.)

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