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Way to use RAID-5 to secure system update

Occasional Contributor

Way to use RAID-5 to secure system update


I want to secure update on Proliant G6 with RAID-5 with spare disk enabled.

I will do :

- stop server
- unplugged 'standby' disk and spare one
- start server

if update succeed :

- hot plug both disk un-plugged

If update failed :

- unplug updated disk
- plug 'standby disk only'
- start server
- hot plug formerly updated disk (RAID will replace data) and hot plug spare one

Do I address this demand in the right way ?
Advice are welcome


Occasional Advisor

Re: Way to use RAID-5 to secure system update

you can do that with a mirrored pair, but not a RAID 5 set
There's no such thing as a stupid question; just stupid people
Jens Ey
Frequent Advisor

Re: Way to use RAID-5 to secure system update

You really can't do this, it will not work.
Btw, there is also a (little) risk that the system crashes in the process of removing a disk from an active array which can result in the loss of data.
You want to do this obviously because you do not have a proper backup of the system. So it would not be useless but a bit dangerous.

1st of all: there is no such thing as a 'standby disk' (that would be a spare disk) in a RAID-5 array. All data are distributed evenly across all 3..n disks of the array. Parity data are added to these data to make the array redundant. The amount of parity data in a RAID-5 is always as large a one disk. Data plus parity of the remaining drives after a single drive failure assemble to the complete data without any redundany.

If you remove the spare drive you remove a drive without any data on it.
If you remove any other drive from the array with n disks you remove 1/(n-1) of the net data capacity of the RAID-5 array. So that would not give you anything usefull.

Advice: Buy an imaging tool from one of the major brands and start doing backups! A RAID array is no replacement for a proper backup!!!