Drobo

Reformat drives during a rebuild?

Can I reformat the drives while it’s rebuilding?

In theory yes - but why would you want to, is it just one volume you want to format?

Practically i’d probably personally wait.

I think doing both simultaneously will result in taking longer time to complete than doing them sequentially (waiting for the rebuild to finish before formatting), but I could be wrong…

i would have thought that since its aware of what’s on it… if you format a volume, then its empty, so the rebuild should finish in seconds (at least for that volume).

in fact - if you are going to format the volume anyway, just delete anything on it - it will speed up your rebuild. then you an format once its done

IMHO trusting the volume bitmap and using that to “shortcut” rebuild time seems dangerous to me, as the bits that are marked unused wouldn’t be redundant (so replacing a drive would lose the ability to correctly undelete files from a point prior to the replacement, for example).

I hope Drobo rebuilds everything, regardless of whether the block is supposedly used by the overlying filesystem or not.

well you know for a fact that it doesnt?

if you put 4 x 2tb drives in a drobo and set up a volume and make a 16tb volume.

then put say 5GB of data on it (i.e. hardly anything)

try pulling and replacing a drive. rebuild should take about 10 minutes, tops (rather than 24-48 hours if it had rebuild the whole missing 2tb drive)

it only rebuilds blocks in use. thats half the beauty of drobo. it not like traditional raid.

also if it had to rebuild “everything” you would never be able to shrink the array would you (for that it needs to rebuild only block in use, on top of blocks marked as free.

If you deleted a LOT of stuff from drobo during a rebuild, it would suddenly become significantly shorter, since it wouldn’t need to rebuild those blocks, it would just discard them[hr]
and blocks marked unused are not redundant, in fact they arent really anything, they are just unused, when you add data it writes them to block and ensures they are redundantly protected.

and no, i would not expect you to be able to undelete files even from a “protected” drobo (i.e. one that hasnt been through a rebuild). you are still thinking too much in terms of traditional raid - where every block is redundantly protected in a predictable fashion. as soon as you delete something from drobo - those blocks are free… one of those could then be used for a redundancy block for the next write, so yes, it would be impossible to “undelete” as it would have been partially overwritten…

@dennx do you mean, just bypassing the rebuild and reformatting to delete all your data at once?

Thanks for educating me yet again Docchris!

So it sounds to be the case that Drobo “recycles” blocks more quickly than non-Drobo storage… I had better make sure I avoid accidental deletions.

This also would mean that keeping the filesystem intact is even more critical in the event of either drive swap or drive loss. Good to know.