[lustre-discuss] Data stored in OST [EXT]

[Peter Grandi]

>> Our last DDN system has OST's using 14TB disks.

> That's quite popular. If single-digit transfer rates per-HDD
> for HPC clusters are the goal, that's ideal :-). [...]

I was just discussing this with someone and they pointed out
that can be a reasonable goal, and indeed it can be, even if not
for HPC clusters, but for archival (something similar to AWS
Glacier) or even cold storage, where low cost matters per TB
more than huge latency or very low bandwidth.

https://blog.dshr.org/2015/03/googles-near-line-storage-offering.html
https://blog.dshr.org/2014/09/more-on-facebooks-cold-storage.html

But given calculations and experience I would still not use
drives larger than 8TB for that, because the IOPS-per-TB of
larger drives are so low that I think that maintenance
operations are hard to do within "reasonable" timeframes.

Overall HDDs with > 8TB capacity are probably best regarded as
"tapes" with the ability to do some random positioning.