michael@xxxxxxxxxxx wrote:
In /etc/fstab, I have entries like this:
UUID=8e651838-38c1-4783-8bde-4174ec484d52 / ext3 defaults 1 1
UUID=aaeca70c-f0fe-470c-b631-87248648d275 /export xfs defaults,nobarrier
1 2
UUID=6e22c5b0-2874-4826-a871-ed733f8da643 swap swap defaults 0 0
UUID=323cd094-4cbe-4c3b-9096-366c05465e7c /export/services xfs defaults 1 2
Do you have an example? I am not sure I follow.
Taken fragment from stock udev rules:
IMPORT{program}="vol_id --export $tempnode"
OPTIONS="link_priority=100"
ENV{ID_FS_USAGE}=="filesystem|other|crypto", ENV{ID_FS_UUID_ENC}=="?*",
SYMLINK+="disk/by-uuid/$env{ID_FS_UUID_ENC}"
ENV{ID_FS_USAGE}=="filesystem|other", ENV{ID_FS_LABEL_ENC}=="?*",
SYMLINK+="disk/by-label/$env{ID_FS_LABEL_ENC}"
- vol_id will export filesystem metadata, which udev will import and
make available for further rules in current uevent
- link_priority will prioritize uuid and label symlinks to the
filesystem found on md0, over existing or to-be-made symlinks
to mirror components. (actully - vol_id called for components will
detect they are part of raid and return md's uuid along with USAGE=raid
- so the link won't be even created in persistant storage rules).
- the rest will create appropriate symlinks
That's the general idea. Of coruse it's only a fragment. Check
60-persistent-storage.rules and 64-md-raid.rules from udev sources, to
see how things get done there.
E.g. in one fstab of mine (not uuids, the same idea though), there're:
/dev/disk/by-id/scsi-SATA_Maxtor_6Y120P0_Y32JMMQE-part1 /boot
ext2 defaults 0 0
/dev/disk/by-id/scsi-SATA_Maxtor_6Y120P0_Y32JMMQE-part2 swap
swap defaults 0 0
So what happens if someone sticks in a USB key and boots the machine.
The key bcomes sda, and each following drive shifts. Is UDEV in this
case going to know to account for this? The goal is to be able to
always find the filesystem regardless of what the disk name might be.
That depends on the udev rules. With typical ones - your names would
shift, but symlinks created from /dev/disk/by-* directories would be proper.
You can even set sd{a,b,c,...} or any other names you want persistently
there, basing on the device's label, uuid or other traits - similary to
how network devices can be named persistently based on e.g. their mac
address. Still - with symlinks - there isn't much reason to.
When mdadm assembles your /dev/md0 - it usually looks for md's uuid
along other things (check your mdadm.conf) - so leaving /dev/md0 in
fstab should be perfectly fine. You can even name it /dev/grubboot - it
doesn't have to be md0.
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