Raid 5 --grow to fewer, larger drivers

Raid 5 --grow to fewer, larger drivers

[Alex Lilley]

Senario:  raid5 with  4 x 120gb.

aim:  raid5 with 3 x 250gb

3 x 120gb disks replaced with 3 x 250gb, array has been rebuilt/resync'd 
at original size. Can we remove the remaining 120gb drive and reshape 
the array over the remaining 3 drives using all the new space.

I guessed --grow --raid-devices=3 --size-max would work but returns "can 
change at most one of size, raiddisks, bitmap and layout"

I then --failed and --remove the remaining 120gb drive and tried --grow 
--raid-devices=3 but receive "Cannot reduce number of data disks (yet)".

I am therefore slightly stumped!

Is this something that is actually possible or something that is planned 
for because as the size of disk drives multiplies and the desire to keep 
tabs of power usage increases it is likely that we will want to reduce 
the number of disk, besides the obvious increased risk of failure 
introduced by having a greater number of drives.

Regards

Alex

Re: Raid 5 --grow to fewer, larger drivers

[Twigathy]

In that situation, I think I'd be happier to hook all the disks up (If
not on the same machine, on two machines on the same [gigE] network,
make a new raid5 on the new set of disks, rsync stuff to the new array
and then retire the old array (Swapping in the array you just
created)... messing around resizing disks for this job just sounds
like mess and risk to me!

Just my £0.02 ;-)

T

2008/11/24 Alex Lilley <alex@redwax.co.uk>:
> Senario:  raid5 with  4 x 120gb.
>
> aim:  raid5 with 3 x 250gb
>
> 3 x 120gb disks replaced with 3 x 250gb, array has been rebuilt/resync'd at
> original size. Can we remove the remaining 120gb drive and reshape the array
> over the remaining 3 drives using all the new space.
>
> I guessed --grow --raid-devices=3 --size-max would work but returns "can
> change at most one of size, raiddisks, bitmap and layout"
>
> I then --failed and --remove the remaining 120gb drive and tried --grow
> --raid-devices=3 but receive "Cannot reduce number of data disks (yet)".
>
> I am therefore slightly stumped!
>
> Is this something that is actually possible or something that is planned for
> because as the size of disk drives multiplies and the desire to keep tabs of
> power usage increases it is likely that we will want to reduce the number of
> disk, besides the obvious increased risk of failure introduced by having a
> greater number of drives.
>
> Regards
>
> Alex
> --
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
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>

Re: Raid 5 --grow to fewer, larger drivers

[Alex Lilley]

That is an interesting work around T, though it does have its own 
issues, namely the need to take the data off-line for the time of the 
copy over the network besides the hassle.

I would be interested to know why there would be any greater 
difficulty/risk in growing to fewer, larger disks than simply growing to 
more disks of the same size.  The problem is that if you have a number 
of disks and need more space, you add another disk of the same size and 
lots of disks will eventually bite you on the bum, so being able to 
consolidate in the way I set out would be a real bonus and nice and 
straight forward (or maybe not!?)

Regarding the risk factor during any array resync, I should hope we all 
have a precious data backed up anyway!

Thanks for you £0.02 though :-)

Alex

Twigathy wrote:
> In that situation, I think I'd be happier to hook all the disks up (If
> not on the same machine, on two machines on the same [gigE] network,
> make a new raid5 on the new set of disks, rsync stuff to the new array
> and then retire the old array (Swapping in the array you just
> created)... messing around resizing disks for this job just sounds
> like mess and risk to me!
>
> Just my £0.02 ;-)
>
> T
>
> 2008/11/24 Alex Lilley <alex@redwax.co.uk>:
>   
>> Senario:  raid5 with  4 x 120gb.
>>
>> aim:  raid5 with 3 x 250gb
>>
>> 3 x 120gb disks replaced with 3 x 250gb, array has been rebuilt/resync'd at
>> original size. Can we remove the remaining 120gb drive and reshape the array
>> over the remaining 3 drives using all the new space.
>>
>> I guessed --grow --raid-devices=3 --size-max would work but returns "can
>> change at most one of size, raiddisks, bitmap and layout"
>>
>> I then --failed and --remove the remaining 120gb drive and tried --grow
>> --raid-devices=3 but receive "Cannot reduce number of data disks (yet)".
>>
>> I am therefore slightly stumped!
>>
>> Is this something that is actually possible or something that is planned for
>> because as the size of disk drives multiplies and the desire to keep tabs of
>> power usage increases it is likely that we will want to reduce the number of
>> disk, besides the obvious increased risk of failure introduced by having a
>> greater number of drives.
>>
>> Regards
>>
>> Alex
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>>     
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