[lustre-discuss] MDT size smaller than expected
Andreas Dilger
adilger at whamcloud.com
Tue Jun 26 05:48:31 PDT 2018
On Jun 26, 2018, at 14:21, Steve Barnet <barnet at icecube.wisc.edu> wrote:
>
> Hi Andreas,
>
>
> On 6/25/18 5:47 PM, Andreas Dilger wrote:
>> On Jun 25, 2018, at 20:39, Steve Barnet <barnet at icecube.wisc.edu> wrote:
>>>
>>> Hi all,
>>>
>>> I'm setting up a new lustre filesystem with 2.10.4. Things are
>>> looking OK so far. However, I noticed that when I mount up
>>> my MDT, df reports a smaller size than I expect. The volume is
>>> 2.2TB, but the MDT reports 1.3:
>>>
>>>
>>> icecube-lfs6-mds-1 ~ # df -h -t lustre
>>> Filesystem Size Used Avail Use% Mounted on
>>> /dev/mapper/md3420-1-vd-0 1.3T 94M 1.2T 1% /mnt/lustre/lfs6-mdt0000
>>>
>>>
>>> It appears that the host sees the correct size for the volume:
>>>
>>> icecube-lfs6-mds-1 ~ # fdisk -l /dev/mapper/md3420-1-vd-0
>>>
>>> Disk /dev/mapper/md3420-1-vd-0: 2388.7 GB, 2388672905216 bytes, 4665376768 sectors
>>> Units = sectors of 1 * 512 = 512 bytes
>>> Sector size (logical/physical): 512 bytes / 512 bytes
>>> I/O size (minimum/optimal): 512 bytes / 512 bytes
>>>
>>>
>>> So I am a little confused. Seems to work OK, but I'd like
>>> to understand what might be going on there.
>> About half of the MDT is consumed by the inodes with the default formatting parameters,
>> so this won't ever show up as part of the free space in the filesystem. The statfs()
>> interface is somewhat limited in what it can show, and the alternative is to show the
>> total blocks as 2.2TB, but there is 1.1TB of "Used" space, which would probably get
>> even more questions on the flip side "why is half of my MDT filesystem used, and how
>> do I get rid of that space usage".
>
>
> Thanks much. So just to make sure I'm clear when the
> inevitable question arises: the total size is 2.2TB,
> however, 1.1TB of that is inodes so that is subtracted
> from the 2.2TB and that's what we see in df.
>
> That makes sense, and I can definitely see why that
> choice would be made. I just wanted to be sure I
> hadn't done something I might regret for the life of
> the filesystem. :-)
No, there is nothing wrong with the system.
---
Andreas Dilger
Principal Lustre Architect
Whamcloud
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