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Old 03-25-2009, 08:27 PM   #1
snoopy1
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Registered: Jun 2007
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RAID and XFS on current filesystem


Hello again,

I've got an XFS filesystem "sda1/sda2". I used mdadm to build a raid 1 array using "sdb1/2" but if I mount md0/md1 then I get..

I/O error in filesystem ("md0") meta-data dev md0 block ox7a90eff ("xfs_read_buf") error 5 buf count 512

I believe this is because software raid adjusts the superblock or something and therefore I need to reformat with xfs again.

My questions are;

a) is it possible to adjust the current xfs partition to work instead of dumping and importing to a new xfs partition

b) if a drive goes down in the future will I be able to mount the drive directly via /dev/sda1 or must it always be mounted via /dev/md0? The reason I ask is I don't know how software raid handles the situation, will it just run on one drive and send a system alert? I was hoping the filesystem was separate to raid so I could go back but it looks like xfs will depend on it. I couldn't therefore take a drive out and mount it if it's using raid.

Thanks for your help,

Andrew
 
Old 03-25-2009, 11:38 PM   #2
vindoan
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Registered: Mar 2009
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1) Yes you can convert an existing partition into a RAID 1 array. The basic steps are:
-Create a single-disk RAID-1 with your new disk
-Copy/move all your data from the old-disk to the new RAID-1 array
-Verify the data move was successful
-Wipe the old disk
-Add the old disk to the new RAID-1 array
-Example at http://wiki.archlinux.org/index.php/...system_to_RAID ; its for ext2 FS, so adopt it according to xfs

2) If a drive goes down in a RAID1 array, it will be marked as dirty. You will still be able to access the array. You can also remove a drive from the system and mount it on another computer. See the software raid how-to simulate a failure. http://tldp.org/HOWTO/Software-RAID-HOWTO-6.html

I suggest you experiment with creating an array with two small partitions, and simulating a failure before you attempt to do this on real data.

Cheers
 
Old 03-26-2009, 10:04 AM   #3
snoopy1
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Registered: Jun 2007
Posts: 44

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Thanks that made sense and worked. You have to reformat a md device with xfs afterwards - you cant use an existing. So I did what you said, copied the xfs partitions (xfsdump & xfsrestore) to sdb, set up a raid 1 device with sda only, dumped the files back onto md0, used the mdadm tool to add sdb as a spare device and then added it to the array.

The "restoring" files onto sdb was rather beautiful to watch.

Cheers,

Andrew
 
  


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