hard disk integrity check

Alan McKinnon alan at linuxholdings.co.za
Wed Apr 19 13:49:45 UTC 2006

On Wednesday 19 April 2006 14:15, Balvinder Kataora wrote:
> > SMART catches about 80% of looming disk errors (according to the
> > SMART people that is). And disk firmware is written to take care
> > of usual errors wherever possible, but it'll never be
> > bullet-proof.
> I never knew that about SMART.

A quick conceptual overview of SMART:

Disks fail mostly for mechanical reasons, and the process is 
well-understood. Motors and bearings wear out, the servos moving the 
head in and out develop play, that kind of thing. Manufacturers have 
huge amounts of data by now on how drives behave as they age, for 
example a very good indicator is spin-up time - how long it takes the 
drive to get up to speed from a standing start. Statistical analysis 
of all this data shows that when a drive starts to take longer than X 
amount of time to get up to speed then the odds of it failing within 
Y hours becomes Z%, so predictions are possible.

What SMART can't tell you anything about is electronic failures. These 
tend to happen without warning, or with no discernible pattern 
beforehand. Lucky for us, they are relatively rare compared to 
mechanical wear.

> This 20Gb drive will be used as an OS disk or to boot the machine
> from. The main user data will be kept on a RAID5 array. Looking at
> the machine I have it seems a RAID1 Mirror set is possible for the
> boot disk. I have little (close to none) long term experience with
> mirrored boot disk, do you think the time invested to create one
> would be beneficial?

I take the view that it depends on your needs. If the machine is 
running a Space Shuttle and absolutely cannot ever fail for any 
reason, then you'd be wise to figure out how to do it. For regular 
use with a good admin nearby and especially if you have a spare drive 
anyway, it's hard to justify the effort. But that's my view, others 
may disagree.

If only you and dead people understand hex, 
how many people understand hex?

Alan McKinnon
alan at linuxholdings dot co dot za
+27 82, double three seven, one nine three five

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