fstab: use UUID or labe?

fstab: use UUID or labe?

[Rory Jaffe]

Question about fault tolerance and choice of ID. I'm running btrfs
with subvolumes for / and /home. /boot and grub are on a thumb drive.
I have six drives in the system, running raid1 for both data and
metadata.

When I run "sudo btrfs fi show" it provides both the label and the
uuid. The UUID shown is the same as that for the first partition that
btrfs was installed on.

In fstab, the mount points currently use that UUID to identify the file system.

If the original drive fails, will that UUID still point to the
filesystem, or is it better to use the label for the filesystem? Will
the filesystem mount in either case with the failure of the original
drive?

Thanks

Rory

Re: fstab: use UUID or labe?

[Chris Murphy]

On Mon, May 4, 2015 at 7:42 PM, Rory Jaffe <rsjaffe@gmail.com> wrote:

> If the original drive fails, will that UUID still point to the
> filesystem, or is it better to use the label for the filesystem? Will
> the filesystem mount in either case with the failure of the original
> drive?

A Btrfs volume has one label and one UUID. All member drives contain
this information. So the answer is, it doesn't matter whether you use
label or UUID in fstab, except that with UUID there's a lower chance
of collision.

-- 
Chris Murphy

Re: fstab: use UUID or labe?

[Austin S Hemmelgarn]

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On 2015-05-04 21:42, Rory Jaffe wrote:
> Question about fault tolerance and choice of ID. I'm running btrfs
> with subvolumes for / and /home. /boot and grub are on a thumb drive.
> I have six drives in the system, running raid1 for both data and
> metadata.
>
> When I run "sudo btrfs fi show" it provides both the label and the
> uuid. The UUID shown is the same as that for the first partition that
> btrfs was installed on.
>
> In fstab, the mount points currently use that UUID to identify the file system.
>
> If the original drive fails, will that UUID still point to the
> filesystem, or is it better to use the label for the filesystem? Will
> the filesystem mount in either case with the failure of the original
> drive?
>
The UUID itself refers to the filesystem as a whole, not that specific 
partition, so even if the original drive fails, the UUID will still 
properly reference the filesystem (whether or not you can mount it is a 
whole separate issue, as a missing device usually means you need some 
manual intervention for recovery).

Personally, I prefer to use labels in fstab, as it makes it much more 
obvious what is what ( and labels are usually much more compact than 
UUID's), although this can cause issues if you aren't careful (multiple 
filesystems with the same label gets really interesting when trying to 
mount by label).  Additionally, on sufficiently recent distributions, 
you might be able to use PARTUUID or PARTLABEL to id individual 
partitions in /etc/fstab, although the disk needs to have a partition 
table format that actually supports this (GPT is the only one I know of, 
although there may be others).



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