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11 June 2013

Learning new fileserver tricks: RAID + LVM

I've finally gotten comfortable with linux's software raid, aka mdadm. I've been hearing about LVM, and I finally took the plunge and figured out how to get the two to play together. Of course, a benefit of RAID is data security. The big benefit I see from LVM is getting to add/remove disk space without repartitioning. Once RAID is working, stacking LVM on top was easy enough, especially for my use case of a single-big-filesystem. I was able to move all my data onto one RAID array, built a new filesystem on top of a logical volume, move data to the new filesystem, and then add the final RAID array to the logical volume and resize the filesystem. Thus, I end up with 3 separate RAID arrays glommed together into a single, large filesystem.

## Tell LVM about RAID arrays 
sudo pvcreate /dev/md2
sudo pvcreate /dev/md3

## Create a volume group from empty RAID arrays
sudo vgcreate VolGroupArray /dev/md2 /dev/md3

## Create a logical volume named "archive", using all available space 
sudo lvcreate -l +100%FREE VolGroupArray -n archive
sudo lvdisplay 
## and create a filesystem on the new logical volume 
sudo mkfs.ext4 /dev/VolGroupArray/archive

## mount the new filesystem
## and move files from the mount-point of /dev/md1 to /dev/VolGroupArray/archive
## then unmount /dev/md1

## Add the last RAID array to the volume group
sudo pvcreate /dev/md1
sudo vgextend VolGroupArray /dev/md1

## Update the logical volume to use all available space 
sudo lvresize -l +100%FREE /dev/VolGroupArray/archive
## And resize the filesystem -- rather slow, maybe faster to unmount it first...
sudo resize2fs /dev/VolGroupArray/archive

## Finally, get blkid and update /etc/fstab with UUID and mount options (here, just noatime)
sudo blkid

I probably should have made backups before I did this, but everything went smoothly...
Also, I discovered this python tool to do conversions in-place. Again, this appears non-destructive, but back-ups never hurt. Also of interest for a file server is Smartmontools to monitor for hardware/disk failures: a nice review is here.


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