[Klug-general] Software Vs Hardware Raid

[J D Freeman]

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On Fri, Jul 04, 2008 at 08:40:57AM +0100, Dan Attwood wrote:
> Surely if you talking about raid and servers the fact that it's portable is
> immaterial?

Portable means more than just easy to move.

It means ability to move stuff about.

Simple example, you have a rack with 3 servers in, each bought a year
apart. Each has a hardware raid device. When the oldest one dies, the
PFY pulls the disks from the machine and puts them in the empty hot swap
bays of the machine above. Which having a RAID card made one year later
has a different firmware, and thus different metadata, thus your drives
are unreadable.

Or, if you just use a hotswap controller in them, you hot add the
drives, and do an mdadm -A magic, and away you go, not even skipping a
beat.

When it comes to users of hardware raid there are two types, those who
have been bitten, and those who will be bitten.

> Being a decently speced raid 5 system means that the chances of total
> failure are greatly reduced and even if it does fail totally you will have
> full backups to restore from.

I personally don't trust RAID5, as my experience is that murphy really
likes to play with hard disks. I use RAID1, Lots of raid1.

# ls /dev/md* | wc -l
158


> As such I would say that hardware is the way to go. Let the board do all the
> work rather then the pc and if the os does stuff up the data should still be
> safe on the data partition where is can be recovered.

As such I would say let software raid do the work. Removes the risks of
hardware fault, and moves all the risk to a highly portable set of
software. Hard disks fail, raid cards fail. The fuckup fairy will come
visit you. Prepare for it as best you can, don't lock youself to one
card.

Julia
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