On Wed, 24 Jul 2013 00:10:31 +0200 Christoph Anton Mitterer <calestyo@xxxxxxxxxxxx> wrote: > On Wed, 2013-07-24 at 06:57 +1000, NeilBrown wrote: > > New feature in 3.3 is that when you reshape (e.g.) a RAID5 to a RAID6 it can > > do so without using a "backup file" - which is are a pain to work with and > > slow things down a lot. > > What it does instead is move the "data_offset" towards the start of the > > device. That way it is never writing onto live data, and so no backup is > > needed. > So you are stealing my precious space, which I was paying soo much money > for?! ;-) > > Seriously,... sounds like a good idea... :) > But why does it also increase the "gap" at the end? Guess the whole > "gap" at the end thingy is something we will never ever really get rid > of, will we? I mean it's no problem because of some missing sectors... > it just makes like more complicated when doing manual geometry > calculations... The "gap at the end" is due to clumsy coding that I indicated earlier that I would try to find time to tidy up. > > > While talking about data_offset... is it planned to implement a way to > add a way to specify the data_offset manually and/or specify a > data_offset_offset (i.e. a additional offset to what mdadm would have > autodetected... similar as LVM allows? You mean like a "--data-offset" option to --create and --grow? Yes mdadm 3.3 has that. > > I mean the practical relevance is probably not that much... but manual > specification would probably needed whenever you have some more complex > block layer (e.g. LVM), another MD or a hardware RAID below MD... and > you want to align to the stripes... or unusual large chunk sizes... > > I've seen that you have some branch where you can specify the offset for > each device... but... guess that was only for some guys to do recovery > works?! It is now part of mainline. NeilBrown
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