Re: raid5 - failed disks

[Frank Wittig <fw@weisshuhn.de>]

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Alvin Oga wrote:
> hi ya raiders ..
> 
> we(they) have 14x 72GB scsi disks config'd as raid5,
> ( no hot spare .. )
> 
> - if 1 disk dies, no problem ... ez to recover

right. if one dies raid does exactly what is's supposed to do...


> - my dumb question is,
> 	- if 2 disks dies at the same time, i

if 2 disks fail at the same time you data is lost.
if you have raid5 with 5 hot spares and a second disk dies, befor a hot
spare is synced into the array (will be listed as spare until sync hast
finished) the same - data gone.


> - i think 4x 300GB ide disks is better ( less likely to fail ?? )

it's a simple calculation.
if one disk fails with a risk of 1 to 100000, then 10 disks fail with 10
to 100000. which means that having 10 disks is two times as dangerous as
having 5 disks.

if i had an array with as much disks as you have i would chose raid
level 6 (not sure if dm supports this by now).
raid level 6 survives two disks failing at once.

btw: what reason is there to switch off air conditioning of your it
equipment. temperature changes are poison to this fragile things.


greetings,
frank

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