> -----Original Message----- > From: linux-raid-owner@xxxxxxxxxxxxxxx [mailto:linux-raid- > owner@xxxxxxxxxxxxxxx] On Behalf Of Alex Lilley > Sent: Tuesday, December 09, 2008 3:12 PM > To: Michael Brancato > Cc: linux-raid@xxxxxxxxxxxxxxx > Subject: Re: status of raid 4/5 disk reduce > > Hi Michael > > I posed this a few weeks back but haven't seen any activity on it yet > or > any suggestion as to when this might be possible. > > For reference, my thread started here: > http://marc.info/?l=linux-raid&m=122753511309332&w=2 > > Cross fingers for this because I think it is a real killer feature. > > Regards > > Alex > > Michael Brancato wrote: > > I'm curious as to the status of the ability to reduce the number of > > disks in a RAID 4/5 array. I would like the ability to reshape a 4 > > disk raid4/5 to a 3 disk raid4/5 for flexibility. > > > > here is what I want to do.... > > $ sudo mdadm /dev/md0 --fail /dev/disk4 --remove /dev/disk4 > > mdadm: set /dev/disk4 faulty in /dev/md0 > > mdadm: hot removed /dev/disk4 > > $ sudo mdadm --grow /dev/md0 -n3 > > mdadm: /dev/md0: Cannot reduce number of data disks (yet). > > > > I know this capability is missing in the md driver. What is needed > to > > make it work and is anyone currently working on it? > > > > Regards, > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid" > in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html This is a lot to ask for in terms of development, and creates extreme risk of data loss. First, you degrade /dev/md0, so any bad blocks or drive failures will cause catastrophic data loss, unless /dev/disk4 is used for mirroring in the interim. Secondly, by removing that disk (for sake of argument, say each disk is 1TB. You go from 3TB usable data to 2TB. Most likely, you need to resize the file system in place so it fits into 2TB. You're probably booted onto md0 also, which makes it difficult. Resizing a hot filesystem without scratch space?? If your file system can't be dynamically reduced, then no point worrying about md raid. I don't see it happening .. ever. Even if somebody wrote the logic, I can't imagine the code being tested enough to be safe for live data. -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
