[ILUG] hard drive workouts - any ideas?

[Ivan Griffin]

Yes, I agree with the points on RAID not being a backup, and the risk of 
accidental deletion etc.  Thats why I have a separate external disk the 
same size as my RAID array that I backup to.

This disk is kept offline mainly to reduce wear & tear, but regularly 
powered up to do the backup and also to prevent stiction.

I've been around the block long enough to appreciate that... but thats not 
my concern here.


What I am interested in is exploiting any techniques in drive firmware 
to encourage them to remap good spare sectors for bad.  Giving the drives 
as much opportunity to do this as possible by regulary reading every sector, 
or possible even bit-inverting every sector and the back again, seems to 
me to be a reasonable strategy.

However, I don't have any experience directly writing drive firmware, 
so I was hoping someone on the list might.

Cheers,
Ivan.


On Sat, 15 Sep 2007, Michael Watterson wrote:

> Yes RAID does not equal backups. It's a tool to reduce downtime and in case 
> of RAID5 increase capacity and performance.
>
> In the 8 years I was designing and responsible for IT systems in a wide range 
> of business there were:
> 2 or 3 disk failures on RAID, no loss of data.
> 2 destroyed RAID systems (One the server knocked over by cleaning staff, and 
> the other jolted while being moved by a so-called technician).
> 1 RAID system with serious downtime for rebuild as the Sales person thought 
> you could unplug a drive from hotswap (without putting it off line first) 
> physically to demo it could lose a drive. Back in 1996 not many Hotswap 
> systems expected anyone to try that without informing the management system 
> 1st. Unplugging a drive is NOT the same as a failure!
>
> Restricted Physical access & mounting is important to stop these things but 
> people won't listen.
>
> Uncountable numbers of events of people deleting databases, spreadsheets, 
> entire sets of accounts. Where we had got the company to pay for backup 
> systems and training to use them, this was not a problem. Where the customer 
> wanted to cut corners it was bad :(
>
> Zero loss of data due to Viruses, Trojans, etc. But that's another story.
>
> Gary Pigott wrote:
>> 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
>>> -- 
>>> Irish Linux Users' Group mailing list
>>> About this list : http://mail.linux.ie/mailman/listinfo/ilug
>>> Who we are : http://www.linux.ie/
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>> 
>
>
> -- 
> Mike
>
> -- 
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