CentOS - Jul 2016 - Mounting NFS subdirectories individually or just the parent?

Hello,

does it in any respect (throughput/performance, cpu load, I/O load, 
resilience, ...) matter, if one mounts subdirectories of an NFS (v3) 
export into separate directories or if one just mounts the parent directory?

I.e. like this:

   server:/export/base/a -> /mnt/a
   server:/export/base/b -> /mnt/b
   server:/export/base/c -> /mnt/c
   server:/export/base/d -> /mnt/d
   server:/export/base/e -> /mnt/e

or simply like this:

   server:/export/base   -> /mnt


I would guess, that it doesn matter at all, but at $work the standard 
setup on all cluster nodes is, to mount >20 subdirectories from the NFS 
server individually and the justification is, that is more performant 
and reliable.

Can this be confirmed (or denied)?

I couldn't find this method of "NFS performance tuning" mentioned 
anywhere and from a management perspective the sheer amount of mounted 
filesystems makes the list confusing and harder to troubleshoot.

Any thoughts?

Regards
frank

On Wed, 27 Jul 2016, Frank Thommen wrote:
> Hello,
>
> does it in any respect (throughput/performance, cpu load, I/O load, 
> resilience, ...) matter, if one mounts subdirectories of an NFS (v3) export
> into separate directories or if one just mounts the parent directory?
>
> I.e. like this:
>
>  server: /export/base/a -> /mnt/a
>  server: /export/base/b -> /mnt/b
>  server: /export/base/c -> /mnt/c
>  server: /export/base/d -> /mnt/d
>  server: /export/base/e -> /mnt/e
>
> or simply like this:
>
>  server:/export/base   -> /mnt
Performance wise, any bottleneck will almost certainly be tied to the 
disks on the back end, not the nfs process itself.

There are a couple good reasons for splitting up the mounts:

1. They can have different export restrictions (e.g., for different
    client hosts, ro vs. rw permissions, user squashing).

2. /base/[a-e] live on different RAID arrays and might benefit from
    different management cycles; that'd also be a case where multiple
    exports might be a good idea. That said, I've never managed an
    exported filesystem consisting of different arrays; we've always
    exported at the RAID level or below.

-- 
Paul Heinlein <> heinlein at madboa.com <> http://www.madboa.com/

There is a slight performance related reason for exporting disk partitions
individually, the performance boost is server-side as Paul says.  The
advantage is that the no_subtree_check can be used without any additional
security risk.

It is probably the case that the /export/base/a is a partition, is exported
with no_subtree_check, and therefore there is a small performance boost.

Preventing server side mount point traversal can also form part of a
security mechanism if servers have different security options for different
mount points, but in this case mounting server:/export/base wouldn't give
you the same client view of the filesystem tree as mounting each
individually if it worked at all.

Cheers,
Sean

On 27 July 2016 at 23:21, Paul Heinlein <heinlein at madboa.com> wrote:
> On Wed, 27 Jul 2016, Frank Thommen wrote:
>
> Hello,
>>
>> does it in any respect (throughput/performance, cpu load, I/O load,
>> resilience, ...) matter, if one mounts subdirectories of an NFS (v3)
export
>> into separate directories or if one just mounts the parent directory?
>>
>> I.e. like this:
>>
>>  server: /export/base/a -> /mnt/a
>>  server: /export/base/b -> /mnt/b
>>  server: /export/base/c -> /mnt/c
>>  server: /export/base/d -> /mnt/d
>>  server: /export/base/e -> /mnt/e
>>
>> or simply like this:
>>
>>  server:/export/base   -> /mnt
>>
>
> Performance wise, any bottleneck will almost certainly be tied to the
> disks on the back end, not the nfs process itself.
>
> There are a couple good reasons for splitting up the mounts:
>
> 1. They can have different export restrictions (e.g., for different
>    client hosts, ro vs. rw permissions, user squashing).
>
> 2. /base/[a-e] live on different RAID arrays and might benefit from
>    different management cycles; that'd also be a case where multiple
>    exports might be a good idea. That said, I've never managed an
>    exported filesystem consisting of different arrays; we've always
>    exported at the RAID level or below.
>
> --
> Paul Heinlein <> heinlein at madboa.com <>
http://www.madboa.com/
> _______________________________________________
> CentOS mailing list
> CentOS at centos.org
> https://lists.centos.org/mailman/listinfo/centos
>

On 07/28/2016 12:21 AM, Paul Heinlein wrote:
> On Wed, 27 Jul 2016, Frank Thommen wrote:
>
>> Hello,
>>
>> does it in any respect (throughput/performance, cpu load, I/O load,
>> resilience, ...) matter, if one mounts subdirectories of an NFS (v3)
>> export into separate directories or if one just mounts the parent
>> directory?
>>
>> I.e. like this:
>>
>>  server: /export/base/a -> /mnt/a
>>  server: /export/base/b -> /mnt/b
>>  server: /export/base/c -> /mnt/c
>>  server: /export/base/d -> /mnt/d
>>  server: /export/base/e -> /mnt/e
>>
>> or simply like this:
>>
>>  server:/export/base   -> /mnt
>
> Performance wise, any bottleneck will almost certainly be tied to the
> disks on the back end, not the nfs process itself.
>
> There are a couple good reasons for splitting up the mounts:
>
> 1. They can have different export restrictions (e.g., for different
>    client hosts, ro vs. rw permissions, user squashing).
I'm not sure you can define individual restrictions for subdirectories 
of exported filesystems?  In our case export permissions are set for 
"server:/export/base".

> 2. /base/[a-e] live on different RAID arrays and might benefit from
>    different management cycles; that'd also be a case where multiple
>    exports might be a good idea. That said, I've never managed an
>    exported filesystem consisting of different arrays; we've always
>    exported at the RAID level or below.
>
Agreed, but this is not the case in our situation.


frank