[lustre-discuss] Lustre Sizing

[Robin Humble]

On Tue, Jan 01, 2019 at 01:05:22PM +0530, ANS wrote:
>So what could be the reason for this variation of the size.

with our ZFS 0.7.9 + Lustre 2.10.6 the "lfs df" numbers seem to be the
same as those from "zfs list" (not "zpool list").

so I think your question is more about ZFS than Lustre.

the number of devices in each ZFS vdev, raid level, what size files you
write, ashift, recordsize, ... all will affect the total space available.
see attached for an example.

ZFS's space estimates are also pessimistic as it doesn't know what size
files are going to be written.

if you want more accurate numbers then perhaps create a small but
realistic zpool and zfs filesystem (using say, 1G files as devices) and
then fill it up with files representative of your workload and see how
many fit on. I just filled them up with large dd's to make the above
graph, so YMMV.

cheers,
robin
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