[lustre-discuss] What does your (next) MDT look like?

[Dilger, Andreas]

On Feb 6, 2018, at 10:32, E.S. Rosenberg <esr+lustre at mail.hebrew.edu> wrote:
> 
> Hello fellow Lustre users :)
> 
> Since I didn't want to take the "size of MDT, inode count, inode size" thread too far off-topic I'm starting a new thread.
> 
> I'm curious how many people are using SSD MDTs?
> Also how practical is such a thing in a 2.11.x Data On MDT scenario?
> Is using some type of mix between HDD and SSD storage for MDTs practical?
> Does SSD vs HDD have an effect as far as ldiskfs vs zfs?

It is worthwhile to mention that using DoM is going to be a lot easier with ZFS in a "fluid" usage environment than it will be with ldiskfs.  The ZFS MDTs do not have pre-allocated inode/data separation, so enabling DoM will just mean you can put fewer inodes on the MDT if you put more data there.  With ldiskfs you have to decide this ratio at format time.  The drawback is that ZFS is somewhat slower for metadata than ldiskfs, though it has improved in 2.10 significantly.

Cheers, Andreas
--
Andreas Dilger
Lustre Principal Architect
Intel Corporation