[lustre-discuss] Experience with resizing MDT

Andreas Dilger adilger at whamcloud.com
Thu Sep 20 13:05:10 PDT 2018

On Sep 19, 2018, at 18:49, Mohr Jr, Richard Frank (Rick Mohr) <rmohr at utk.edu> wrote:
> Has anyone had recent experience resizing a ldiskfs-backed MDT using the resize2fs tool?  We may be purchasing a small lustre file system in the near future with the expectation that it could grow considerably over time.  Since we don’t have a clear idea of how many inodes we might need in the future, I wanted to consider options that would allow us to potentially expand the MDT capacity over time.  (Of course, using ZFS would allow us to easily expand capacity, but I do have some concern about metadata performance.  Also, we will likely need to use project quotas which as far I remember is not available for ZFS at the moment .)

I've used resize2fs to resize my MDT in the past, but this was for relatively small resize increments, and I haven't done it recently.  Note that for Lustre MDT/OST mounts, you can't resize the filesystem directly while mounted.  It is possible to *also* mount the filesystem as type ldiskfs to run the resize2fs command (basically to give it a place to call the resize ioctl()), but YMMV.

It is always a good idea to have an MDT backup (every few days if possible) since it is a relatively small amount of space to store an MDT backup, which may avoid a large amount of data loss/restore.  Even a "dd" backup of the live MDT is likely usable after e2fsck, and better than a broken MDT if something goes wrong.

Cheers, Andreas
Andreas Dilger
Principal Lustre Architect

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