[Lustre-discuss] 8T Limit

[Peter Grandi]

> I recall that there is an 8T limit on the size of an OST.  Is
> that just for Lustre 1.6?  Or also 1.8 and 2.0? Now that we
> are starting to get 2T drives, is there any way to exceed 8T?
> Thanks. [ ... ]

While I have seen Lustre developers recommend having few large
OSTs, queries like this seem to me to be based on assuming that
'fsck' (or "resilvering" in the futurea) of the OSTs is never
needed. Good luck with that.

One of the advantages of Lustre, which applies regardless of the
clustering aspect, is that OSTs can be checked in parallel.

There is a good argument that for 'fsck' purposes file systems
should not be larger than one disk; because 'fsck'ing, unlike
large or parallel reading or writing, does not scale well on
RAID, and the ratio of disc arms per TB is ever shrinking.

Sure, OSTs have a significant fixed overhead in Lustre, yet
Lustre implementors should consider carefully how long their
clients are prepared to wait for a damaged OST to be checked or
reloaded from backup.