Re: Raid: software or hardware

Matthew Wild <M.Wild@xxxxxxxx> writes:
Personally, I've generally preferred hardware RAID. I've had software
RAID systems not notice a drive failing,

Which software RAID was that?

causing corruption of the
filesystem.

How does not noticing a failing drive cause the corruption of the file
system?

The better hardware RAID cards seem to be better at sniffing
out a failing disk and removing it from an array before any problems can
ensue.

What kind of sniffing and problems are you imagining? If a disk
fails, that's a very obvious thing (it either delivers errors or does
not talk to the controller at all), and a RAID (except RAID0) is there
to prevent problems from failing disks. Even SMART data is not very
good at predicting disk failures (cf. the Google study), and anyway,
with a RAID you can afford to wait until it really fails.

If a drive fails, software and hardware RAID are equivalent. Simply
replace the drive. The md software in Linux will automatically rebuild
the drive as needed. The "hardware" solution? Who knows, but we presume
it will do the same.

All hardware RAID systems I've used do this and more. They'll even
e-mail you with any alerts on the system.

Is that something special? Look up "mdadm --monitor --mail".

The real difference is what happens if you suffer a controller failure.
Typically, if using hardware RAID (say RAID 5), you will have to replace
the mainboard/controller with an EXACT match. Which puts a lot of trust
in your vendor. With Software RAID, you put the drives into a compatible
Linux box, and things "just work".

I wouldn't have thought this is such a major problem if you use a major
RAID system vendor. 3Ware or Areca are likely to be around for a while.

Maybe. But will they still have that RAID system on offer? And how
long does it take you to get it? If you don't have the replacement
on-site that means quite a bit of downtime.

BTW, the OP was not asking about a 3Ware RAID controller, but about a
JMicron on-motherboard controller. Who knows how long JMicron will be
around, and whether it will be possible to get a compatible RAID
controller or motherboard when the first one dies in a few years.

For really important data systems, you should be thinking of having
spares ready to be installed, or go for a proper external RAID system
with hot-swap everything and support contracts to match.

Yes. For every server we buy, we buy a second one as a spare. We do
not spend a lot of money for redundancy within each server, except for
an md RAID1, which is cheap.

However, I doubt that the OP is in the market for that.

- anton
--
M. Anton Ertl Some things have to be seen to be believed
anton@xxxxxxxxxxxxxxxxxxxxxxxxxx Most things have to be believed to be seen
http://www.complang.tuwien.ac.at/anton/home.html
.

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