On Wed, 29 May 2013 14:13:13 +0100 Mark Rogers mark@quarella.co.uk allegedly wrote:
On 29 May 2013 12:01, mick mbm@rlogin.net wrote:
I have been following this discussion with some interest (and concern) because I have just a week or so ago built my first debian based software RAID server.
Well the first thing to say on this would be: think about how different the RAID threads would have been had myself or Chris not used RAID. In Chris' case, his one lost disk would have meant a loss of his data; in my case the RAID appears to have mirrored some filesystem corruption between two disks. So for Chris, RAID has saved his bacon, and for me it's wither helped or made no difference - it certainly hasn't made things worse.
At the end of the day your data is safe until (a) the hardware fails or (b) it gets corrupted. RAID helps with (a) as long as you monitor it, otherwise when one disk fails you don't deal with it. RAID doesn't help with (b) (nor does it cause it) which is why backups are important. After all, having two perfectly mirrored copied of a virus isn't all that helpful!
Good point. My previous NAS setup had two separate backups for my crucial data. One to the D-Link NAS (a RAID 1 setup) and a second to one of the NSLU2s (non-RAID). Less important data (e.g. MP3s and MP4s where I have the CD or DVD) was backed up up to other devices. (See previous discssions about rsync...) Now that I have centralised my storage I think I had better keep another backup device going.
I am now investigating how best to monitor the disks using smartctl!
First thing is to make sure you're getting notifications from RAID. This should just be a case of making sure your system can send emails and then putting your email address in /etc/mdadm/mdadm.conf (set the MAILADDR parameter).
Mine was left set to the default: "root", a mailbox which isn't checked. Make sure you can send emails from the command-line: mail <insert your chosen address here> .. and follow the prompts, making sure you're able to send (and receive!) the email. (Apologies for the sucking eggs lesson but there'll be someone reading this that might need it).
No apology necessary. It prompted me to check that mail was operational on the new box (errm it wasn't, but it is now).
As an aside: I always use software RAID (mdadm) these days. When the host hardware fails, taking the disk out and putting it into any other Linux box is easy (eg via a USB caddy), which is not the case when using either hardware RAID, or the software RAID that comes on some motherboards and SATA cards. Genuine hardware RAID has its performance advantages but I don't generally work in environments where that's necessary.
The new box has a motherboard which offers "fake-raid". I decided (partly based on previous discussions on ALUG) that mdadm looked a better supported option. Having played with it on the aforementioned retired box I decided to take the plunge and build a new server. That turned out to take longer than it should because the new motherboard has UEFI rather than good old fashioned BIOS. This was my first build with UEFI.
Also, contrary to what many people suggest, I prefer to use non-identical drives in my RAID arrays. Two identical drives from manufacturer A may be very compatible but will also be at risk of failing at very similar times due to their identical manufacturing processes. A drive each from mfrs A and B makes more sense to me. Just be aware that two disks of the same "size" often aren't identical sizes so make sure the partition size you create fits on both disks.
Interesting (and plausible) theory.
Many thanks for the feedback.
Mick ---------------------------------------------------------------------
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