On Mon, Feb 18, 2019 at 2:00 PM Markus Schaufler <markus.schaufler@digit-all.at> wrote:
Hi all,

I've got a design question:
Are there any best practices regarding NFS datastores especially datastore sizing? Should I use one big NFS datastore and expand it on demand or should the size not exceed a certain limit and start with a new NFS datastore?

Unless you have a reason to use multiple storage domains, like separating storage for
different groups (production,testing, development) less storage domain is best. Every storage
domain includes monitoring and ioprocess child process so you don't want to create many
storage domain for no reason.

We don't have any limit on the size of a storage domain. We do support up to 50 storage
domains.
 
Are there any other configuration considerations (NFS v3 or v4(.1) and mounting options)?

I think the only NFS version that should be used now is 4.2. It gives *huge* performance
improvements because it supports sparseness.

Here are some examples:
- creating preallocated disk is instant, instead of minutes/hours (depending on disk zie)
  with NFS < 4.2
- copying preallocated disks can be much faster because qemu can read only the allocated
  parts and can zero unallocated parts instantly.

You can see here how much faster is copying raw disk from NFS 4.2 vs block storage:
https://bugzilla.redhat.com/show_bug.cgi?id=1511891#c57

Coping here the relevant part:

## Copying from NFS 4.2 to FC storage domain
...
image       qemu-img    qemu-img/-W      dd    parallel-dd
----------------------------------------------------------
100/19G          242             41      165           128

## Copying from FC storage domain to FC storage domain
...
image       qemu-img    qemu-img/-W      dd    parallel-dd
----------------------------------------------------------
100/19G          383            194      178           141
As you can see, copying from NFS 4.2 was 4.5 times faster (41 vs 194). When
copying from NFS to NFS the difference is much smaller (242 vs 383).

You can add mount options if you have special needs via engine UI or REST API / SDK.

Nir