Re: (clug-talk) Removing RAID 1??

[Kevin Anderson]

It certainly should... Afterall, that's the purpose of RAID1, right?   I've never used Linux's software RAID, the whole purpose is so that if 1 drive is gone (usually due to failure), the system just keeps going.  Making it an intentional failure shound't matter.   I've used this as a backup during OS upgrades even.  I'd pull the mirror set, then if the upgrade went smoothly, readd it, and let it mirror back up overnight.  If the Upgrade failed, the backout plan was really fast, and super reliable.  Pull the upgraded drives, and insert the originals.  Remirror overtop of the upgraded ones.  It works great.   One thing to keep in mind is that (at least with some software RAID) you need to be sure which drive you take out.  It is possible that when you put the second drive back, if 1 drive is consitered the master, then when the RAID set rebuilds itself, it'll completely overwrite the other drive.  If the OS consiters the drive you used elsewhere to be the master, you'll be in a world of hurt if it completely overwrites the drive that remained in production.   Again, I've never worked with Linux's OS RAID, so don't take my word for it.  But that IS the purpose for RAID 1 afterall.  Well, Fault tolerance and performance...  There is no faster drive setup than mirroring.  (and no, RAID 5 doesn't even come close. (well, it does come fairly close on writes, but not on reads.))  It's just really expensive because rather than n+1, you have n*2 drives.  And you run out of space for 'em pretty fast on a big array.  So expect a performance hit if the server is heavily used...   Kev.       ----- Original Message ----- From: Johnny Stork To: CLUG Sent: Monday, October 28, 2002 8:24 PM Subject: (clug-talk) Removing RAID 1?? I am about to begin a long needed rebuild of some servers and will be moving some drives around. One machine runs software RAID-1 on RH 7.3 with two identical 20gb drives. 3 partitions mirrored, /boot, / and swap. I would like to avoid having to take down all three servers for the ???? days it will take to rebuild them so can start the process if I can "steal" one of the mirrored drives on this machine. Is it possible to simply remove the second, mirrored drive and make some changes somewhere, fstab? and keep the system up while I use the removed drive? Here are the contents of my raidtab and fstab if that helps. raidtab contents: raiddev /dev/md0 raid-level 1 nr-raid-disks 2 chunk-size 64k persistent-superblock 1 nr-spare-disks 0 device /dev/hda2 raid-disk 0 device /dev/hdc2 raid-disk 1 raiddev /dev/md1 raid-level 1 nr-raid-disks 2 chunk-size 64k persistent-superblock 1 nr-spare-disks 0 device /dev/hda1 raid-disk 0 device /dev/hdc1 raid-disk 1 raiddev /dev/md2 raid-level 1 nr-raid-disks 2 chunk-size 64k persistent-superblock 1 nr-spare-disks 0 device /dev/hda3 raid-disk 0 device /dev/hdc3 raid-disk 1 fstab contents: LABEL=/ / ext3 defaults 1 1 LABEL=/boot /boot ext3 defaults 1 2 none /dev/pts devpts gid=5,mode=620 0 0 none /proc proc defaults 0 0 none /dev/shm tmpfs defaults 0 0 /dev/md2 swap swap defaults 0 0 /dev/fd0 /mnt/Floppy auto noauto,owner,kudzu 0 0 /dev/cdrom /mnt/CD-Rom iso9660 noauto,owner,kudzu,ro 0 0 ________________________________________ Johnny Stork Calgary, AB Canada Open Solutions Open Source & Linux Solutions for Business http://www.open-solutions.ca http://www.opensourceinfo.net http://www.penguinportal.net Academic Computers http://www.academic-computers.com