NFSv3 and SYNC option

NFSv3 and SYNC option

[przemyslaw_sowa]

Hello,

I'd like to know if the "sync" option in /etc/exports makes NFSv3 works
like NFSv2? I mean if it then always waits for the data to be written to
the drive before sending reply?

If not, is there any way to guarantee stable storage on the server (v3)
side (ex. client can mount with the async option)?

Regards,
Przemyslaw Sowa



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Re: NFSv3 and SYNC option

[Trond Myklebust]

On Mon, 2006-07-17 at 11:11 +0200, przemyslaw_sowa@o2.pl wrote:
> Hello,
> 
> I'd like to know if the "sync" option in /etc/exports makes NFSv3 works
> like NFSv2? I mean if it then always waits for the data to be written to
> the drive before sending reply?

No. The 'sync' option just ensures that all RPC calls that require data
to be put to stable storage are honoured. The result is that you should
be guaranteed correct recovery semantics in case of a server
crash/reboot (which is what you want).

> If not, is there any way to guarantee stable storage on the server (v3)
> side (ex. client can mount with the async option)?

Yes. NFSv3 has protocol support for safe server-side cached writes (this
is the main reason why NFSv3 is considered to be faster than NFSv2). By
"safe", I mean that there is no loss of data in the case of a server
crash/reboot.
This caching behaviour is enabled by default: no need for additional
mount options.

Cheers,
  Trond



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