On Tue, 12 Apr 2011 18:21:13 +0100 Mathias BurÃn <mathias.buren@xxxxxxxxx> wrote: > If I use --layout=preserve , what impact will that have? > If I preserve the layout, what is the final result of the array > compared to not preserving it? Neil wrote about this on his blog: "It is a very similar process that can now be used to convert a RAID5 to a RAID6. We first change the RAID5 to RAID6 with a non-standard layout that has the parity blocks distributed as normal, but the Q blocks all on the last device (a new device). So this is RAID6 using the RAID6 driver, but with a non-RAID6 layout. So we "simply" change the layout and the job is done." http://neil.brown.name/blog/20090817000931 Admittedly it is not completely clear to me what are the long-term downsides of this layout. As I understand it does fully provide the RAID6-level redundancy. Perhaps just the performance will suffer a bit? Maybe someone can explain this more. If anything, I think it is safe to use this layout for a while, e.g. in case you don't want to rebuild 'right now'. You can always change the layout to the traditional one later, by issuing "--grow --layout=normalise". Or perhaps if you plan to add another disk soon, you can normalise it on that occasion, and still gain the benefit of only one full reshape. > Will the array have redundancy during the rebuild of the new drive? If you choose --layout=preserve, your array immediately becomes a RAID6 with one rebuilding drive. So this is the kind of redundancy you will have during that rebuild - tolerance of up to one more (among the "old" drives) failure, in other words, identical to what you currently have with RAID5. -- With respect, Roman
Attachment:
signature.asc
Description: PGP signature
