[ILUG] hard drive workouts - any ideas?

[Gary Pigott]

Hi Ivan,

to be honest, RAID is over rated when it comes to backup. RAID is for HA 
where you need to be able to tolerate a failure and stay running, but it 
isn't backup. Hard drives do just go bang and RAID will save your data, but 
you're stuffed if you/others delete, or the OS corrupts, a file that you 
created/modified since you last did your manual backup to an external drive. 
The RAID controller will ensure data will get deleted/trashed on the second 
disk at the same time. I see this happen a lot more than dramatic drive 
failures.

Rather than have a pair of drives in a RAID set, I prefer to set them up as 
individual drives with the second one *only* mounted during a backup or 
restore. Having a permanently connected "backup" drive means you can do more 
frequent, more automated, less intrusive backups. Write a script that mounts 
hdb, does an rdiff-backup and then umounts it again. rdiff will do an 
incremental backup and preserve the older versions rather than overwriting 
them. Stick it in the crontab to run as often as you like and you're nicely 
covered. If you want to be even more secure, use rdiff to push the data to a 
remote site (like Skynet) too.

What you call "regular testing", I call "wearing out". I'd just leave the 
disks alone and be sure my data is protected *when* a disk dies, rather than 
putting additional wear and tear on them to make them fail earlier, with the 
hope that SMART (or more manual methods) will detect the failure in time. 
Only 30% of drive failures are detectable by SMART if you believe Wikipedia 
(see http://en.wikipedia.org/wiki/S.M.A.R.T.#Background). If you're running 
hardware RAID, Linux will only see one "disk" as it'll all be hidden by the 
RAID controller, so there's a limit to the efficacy of any disk diagnostics 
you can script within the OS. A good RAID controller will have an 
interactive diagnostic function in firmware that you can run during boot.

Gary


--------------------------------------------------
From: "Ivan Griffin" <ivan at skynet.ie>
Sent: Friday, September 14, 2007 10:49 PM
To: <ilug at linux.ie>
Subject: [ILUG] hard drive workouts - any ideas?

>
> Hi All,
>
>
> I've recently become very paranoid about my data, after having lost a 
> drive to catastrophic failure.
>
> My important docs are now in RAID, and backed up weekly to a drive I keep 
> mostly offline and offsite.  My home NAS box is Sparc (LEON) based, and 
> runs Linux.
>
> I run smarttools on the box, although I'm not expecting much from 
> S.M.A.R.T.
>
> I am interested in strategies suitable for running from a cronjob to give 
> the drive firmware a good workout, and a chance to map out any bad blocks 
> that show up.
>
> Is there any merit in cron'ing something like dd if=/dev/hdX of=/dev/null 
> bs=XXXX ?
>
> What about going a step further, and running a tailored initrd to read 
> each sector, xor with a bit pattern, write, compare, xor out the pattern, 
> write, compare ...
>
> I've searched for literature on this type of thing, but not found anything 
> of note, other than some marketing blurb on GRC's spinrite.
>
> Do people have experience of this? Anyone work directly on drive firmware? 
> What works best for the drive?
>
>
> Best Regards,
> Ivan
> -- 
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