[lustre-discuss] ZFS mdt
Hans Henrik Happe
happe at nbi.dk
Mon Jan 27 12:54:10 PST 2020
Obviously it depends on the number of inodes (files,dirs etc) you have.
However, if the zfs pool uses ashift=12, which will be the default for
most SSDs and large HDDs, it can have quite an overhead for MDTs. It
takes a lot of bandwidth on MDTs if you do a lot of metedata operations.
You can check it by running 'zdb |grep ashift'.
We are using ashift=9 on SSDs for this reason, even though the SDDs
would prefer it differently.
On 27.01.2020 19.07, Nehring, Shane R [LAS] wrote:
> Hey all,
> We've been running a lustre volume for a few years now and it's been
> working quite well. We've been using ZFS as the backend storage and
> while that's been working well I've noticed that the space usage is
> a little weird on the mdt:
> NAME PROPERTY VALUE SOURCE
> store/work-mdt used 4.91T -
> store/work-mdt logicalused 960G -
> store/work-mdt referenced 4.91T -
> store/work-mdt logicalreferenced 960G -
> store/work-mdt compressratio 1.00x -
> Just wondering if anyone else has noticed this kind of overhead.
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