Re: Maximal volume size for the client with a NFS v3 mounting
On 09/28/2016 07:18 PM, Jean-Paul Bouchet wrote:
> On a Jessie 8.5 system I mount a partition on a NAS server with NFSv3
> protocol using options "nfs rw,soft" in /etc/fstab.
>
> The size of the volume on the NAS server side has been extended to 20
> To, but for my Debian system, this extension appears to be limited to
> 16 To :
> - The df command gives 16106127360 blocks of 1K
> - processes trying to write beyond this limit end with error "no
> space left on device"
>
> Is the volume size mounted with NFSv3 limited to 16 To on the client
> side ?
RFC 1813 (the NFSv3 standard) defines the field for the free
space in the response of a NFSv3 server to be a 64bit (probably
unsigned) integer, so that should easily hold more than 16 TiB.
In your case, the 16 TiB limit you experience seems to be if
the size is somehow measured in a 32bit field in units of 4 KiB
blocks. From reading the source code, Linux 3.16 (that comes
with Jessie) only uses 64bit fields in both the NFS client code
and the general kernel structures, so I believe you're running
into a limitation of the NFS server your NAS provides.
I am not sure though - and I don't have any storage with more
than 16 TiB lying around to actually test it - so take my
response as an educated guess based on my read of the kernel
source code.
> Could the version 4 of NFS solve this problem ?
Possibly; it could be that the NFS4 implementation of your NAS
is not limited in that way - it could also be that it is. It
could also be that the NFS server in your NAS doesn't support
volumes > 16 TiB at all.
Another possibility could be that your NAS's NFS server supports
more than 16 TiB just fine, but the underlying filesystem used
on the NAS only supports up to 16 TiB. (For example, if the NAS
were to use the old Linux filesystem ReiserFS, that only supports
volumes up to 16 TiB.) Does the NAS actually show that there's
that much space free on the filesystem it exports? Or does it
only see the 20 TiB on the partitioning level? What NAS are you
using and what software are you running there?
Regards,
Christian
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