Enterprise Volume Management System

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EVMS Frequently Asked Questions

Volume setup and design

Q. I just have a single disk in my computer now. How can I use EVMS to better manage my storage space? How can I configure my volumes so I could add new disks later and use that space in the existing volumes?

A. Answer coming soon.

Q. I have two disks in my computer and I would like to set up a mirror to protect against a disk failure. What is the best way to configure my volumes?

A. Answer coming soon.

Q. I have several disks in my computer and I would like to set up a RAID-5 device to protect against a disk failure. What is the best way to configure my volumes?

A. Answer coming soon.

Q. I just put a new disk in my system but it doesn't show up in the list of Available-Objects. How do I paritition my disk?

A. The new disk most likely will show up in the Volumes list as a Compatibility Volume. For example, a brand new disk "sda" would show up as "/dev/evms/sda". You simply need to delete the volume and the disk then will show up in Available-Objects. You then can use the disk to create other objects and volumes.

Volume activation

Q. I'm running on a 2.6 kernel and some or all of my volumes fail to get activated. The volumes don't show up in the /dev/evms/ directory and I get the following errors in my kernel log:

device-mapper: dm-linear: Device lookup failed
device-mapper: error adding target to table

A. You probably need to apply the bd-claim patch to your kernel. See http://evms.sf.net/install/kernel.html#bdclaim for more details about this patch and other possible options.

System Startup

Q. I rebooted my system, and during boot-up it complains about not being able to fsck the root volume. The boot-up stops and it drops to a root shell prompt. What happened to my root volume?

A. To get your system back to a normal state, run the following commands from the root shell prompt:

mount -o remount,rw /
/sbin/evms_activate

Then reboot your system once more and it should boot normally.

The reason for this behavior is due to the order in which Device-Mapper devices are activated. DM assigns device-numbers dynamically as devices are activated. If you made a change to your volume configuration, it's possible that it changed the order in which EVMS discovers and activates all the DM devices. However, the device nodes in /dev/evms/ represent the device-number assignments from the previous boot. Since evms_activate usually doesn't run until after the root-filesystem is remounted read-write, the device node for your root volume may have the wrong device-number. Thus the error when it tries to fsck the root volume.

One of the best solutions to this problem is to use udev to manage your /dev directory, and to mount a tmpfs on /dev. With this type of setup, you can actually have your boot scripts run evms_activate before the root filesystem is fsck'ed and remounted read-write. This ensures that the /dev/evms/ directory is correctly up-to-date with the current DM device-number assignments before the root volume needs to be fsck'ed.

Software RAID

Q. I have a RAID-5 region, and My system was running fine but got shut down uncleanly. Now EVMS says my RAID-5 is corrupted and no longer activates it. How do I recover my region?

A. Answer coming soon.

Q. I have a RAID-0 or RAID-5 volume with a JFS or XFS filesystem. I would like to expand my RAID volume by adding another disk. EVMS says the RAID volume must be inactive in order to expand, but it also says that JFS and XFS must be mounted in order to expand. How can I expand my RAID volume?

A. This is definitely an unfortunate catch-22. Luckily there's a pretty simple workaround. All you need to do is fool EVMS into thinking there isn't an XFS or JFS filesystem on your RAID-0 or RAID-5 volume just during the time that you want to expand it. To do this, move the appropriate plugin library (XFS and/or JFS) out of /lib/evms/x.y.z/ to some temporary location. Then run the EVMS UI, and since the XFS/JFS plugin isn't loaded, it won't detect the filesystem. Then you'll be able to expand the RAID volume. After the RAID expand is complete, you'll just need to manually expand the XFS or JFS filesystem (after mounting it). For XFS, use the xfs_growfs command. For JFS, you simply remount the filesystem using the command mount -o remount,resize /mnt/point. After this, you can move the XFS/JFS plugins back to the /lib/evms/x.y.z/ directory.

Snapshots

Q. I've taken a snapshot of my XFS file system. If the original volume is unmounted, I can mount the snapshot without any problem. However, if I try to mount the snapshot while the original is mounted, I get the following error:

mount: wrong fs type, bad option, bad superblock on
/dev/evms/Snapshot or too many mounted file systems.

A. XFS does internal checking to prevent one file system being mounted multiple times. Because the snapshot looks exactly like the original, XFS assumes you're trying to mount the same file system twice. You can prevent this behavior by using the "nouuid" option to the mount command.

mount -o nouuid /dev/evms/Snapshot /mnt/Snapshot

Other Plug-ins

Q. I get the following message when I start any of the EVMS user interfaces:

Engine: The plugin Ext2/3 in module /lib/evms/libe2fsim.1.2.1.so
requires the Engine services API version (8.1.0), which is less than this
Engine's services API version (12.0.0).
Engine: The plugin failed to load.

A. The e2fsprogs package includes its own plug-in for EVMS. However, this plug-in is not up-to-date with the latest EVMS internal interfaces. Because the EVMS package comes with its own version of the Ext2/3 plug-in, the plug-in that comes with e2fsprogs (/lib/evms/libe2sfsim.1.2.1.so) can simply be deleted.