This is a refershing info, depressing is the fact that a slice can't be added unobrtusively ( sp ?), I'll try Luca's solution first than scratch & rebuild if this will be a resounding failure ;).
-----Original Message-----
From: linux-raid-owner@vger.kernel.org [mailto:linux-raid-owner@vger.kernel.org] On Behalf Of Cress, Andrew R
Sent: Wednesday, January 07, 2004 9:48 AM
To: Catalin BOIE; Mircea Ciocan
Cc: linux-raid@vger.kernel.org
Subject: RE: Please help with a special RAID 1 setup
Note that RAID-1 will only ever have a maximum of 2 active disks.
I don't believe that the above is a correct statement. Linux software RAID1 will allow mirroring across more than 2 devices:
[root@cinshrlnxlap01 ~]# cat /proc/mdstat Personalities : [raid1] read_ahead 1024 sectors md2 : active raid1 [dev 01:02][2] [dev 01:01][1] [dev 01:00][0] 4032 blocks [3/3] [UUU]
[SNIP]
Ha, so I'm not the only one crazy enough to propose such a solution, I'm happy that I'm not alone :), did it worked ??We had a "triple" mirror sofware RAID setup on a box as a "poor man's snapshot" before we started using LVM. We triple mirrored and then broke one mirror to backup and then added the removed disk back into the array and re-synched. LVM snapshots are much more elegant and LVM provides more functionality such as extended volumes when you want to add more space. You have to be careful using LVM because as of 2.4.18 there was a Linux VM bug that would not allow snapshotting with greater than about 6GB of system RAM.
However, I would recommend recreating the filesystem on top of LVM and using snapshots to accomplish what you want. We use LVM on top of SW RAID with great success.
I belive that was designed and initialised from the first time as a 3 slice raid, the 3rd slice wasn't aded as an aftertought ??
The raid boxes have 4GiB RAM so is not a problem, BTW to you have a pointer for starting the RTFM about that LVM and especially those snapshots, is there a posibility to to save the inital setup with 2 slices or everything has to be destroyed and recreated again???
Best regards,
Mircea
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