Re: Ceph doesn't update the block device size while a rbd image is mounted

[Wido den Hollander <wido@widodh.nl>]

Hi,

On 19-07-12 16:55, Sébastien Han wrote:
> Hi Cephers!
>
> I'm working with rbd mapping. I figured out that the block device size
> of the rbd device is not update while the device is mounted. Here my
> tests:
>

iirc this is not something RBD specific, but since the device is in use 
it can't be re-read by the kernel.

So when you unmount it the kernel can re-read the header and resize the 
device.

Wido

> 1. Pick up a device and check his size
>
> # rbd ls
> size
>
> # rbd info test
> rbd image 'test':
> size 10000 MB in 2500 objects
> order 22 (4096 KB objects)
> block_name_prefix: rb.0.6
> parent:  (pool -1)
>
> 2. Map the device
>
> # rbd map --secret /etc/ceph/secret test
> # rbd showmapped
> id pool image snap device
> 1 rbd test - /dev/rbd1
>
> 3. Put a fs on it and check the block device size
>
> # mkfs.ext4 /dev/rdb1
> ...
> ...
>
> # fdisk -l /dev/rbd1
>
> Disk /dev/rbd1: 10.5 GB, 10485760000 bytes
>
> 4. Mount it
>
> # mount /dev/rbd1 /mnt
> # df -h
> /dev/rbd1                   9.8G  277M  9.0G   3% /mnt
>
>
> 5. Change the image size
>
> # rbd resize --size 11000 test
> Resizing image: 100% complete...done.
>
> # rbd info test
> rbd image 'test':
> size 11000 MB in 2750 objects
> order 22 (4096 KB objects)
> block_name_prefix: rb.0.6
> parent:  (pool -1)
>
> At this point of time, if you perform the fdisk -l /dev/rbd1, the
> block device size will remain the same.
>
> 6. Unmount the device:
>
> # umount /media
>
> # fdisk -l /dev/rbd1
> Disk /dev/rbd1: 11.5 GB, 11534336000 bytes
>
> Unmounting the directory did update the block device size.
>
> Of course you can do something really fast like:
>
> # umount /media && mount /dev/rbd1 /media
>
> That will work, it's a valid solution as long as there is no opened
> file. I won't use this trick in production...
>
> I also tried to "mount -o remount" and it didn't work.
>
> 7. Resize the fs (this can be performed while the fs is mounted):
>
> # e2fsck -f /dev/rbd1
> e2fsck 1.42 (29-Nov-2011)
> Pass 1: Checking inodes, blocks, and sizes
> Pass 2: Checking directory structure
> Pass 3: Checking directory connectivity
> Pass 4: Checking reference counts
> Pass 5: Checking group summary information
> /dev/rbd1: 11/644640 files (0.0% non-contiguous), 77173/2560000 blocks
>
> # resize2fs /dev/rbd1
> resize2fs 1.42 (29-Nov-2011)
> Resizing the filesystem on /dev/rbd1 to 2816000 (4k) blocks.
> The filesystem on /dev/rbd1 is now 2816000 blocks long.
>
>
> Did I miss something?
> Is this feature coming?
>
> Thank you in advance :)
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