throttling NFS writes

nmh drumslayer2 at
Sat Nov 19 02:24:29 GMT 2005

--- Mikhail Teterin <mi+mx at> wrote:

> Hi!
> We have an unusual problem with NFS writes being
> _too fast_ for our good.
> The system is accepting database dumps from
> NFS-clients and begins compressing 
> each dump as soon, as it begins arriving (waiting
> for more via kevent, if 
> needed).
> The NFS-clients (database servers) run on slow Sparc
> processors and can not be 
> bothered to compress their data...
> The setup works quite well, if the to-be compressed
> data is still in memory, 
> when the compressor gets to it.
> "Unfortunately", those Sparc systems have rather
> fast I/O rates and manage to 
> write their dumps faster, than the compressor can
> compress it. When this 
> happens, the overall performance of the backup
> script goes down through the 
> floor :-(, because it forces the disk to read the
> middle of a file (for 
> compression), while data keeps arriving (from the
> NFS-client) at the end of 
> it...
> So we'd like to stall the client's dumping, so that
> the compressor can keep 
> up. Short of limiting NFS-bandwidth via ipfw, is
> there a way to control NFS 
> speed dynamically?
> The uncompressed dumps are _huge_, although they
> compress very well. So we can 
> not just accept all of them first and then start
> compressing -- we don't have 
> enough room. There is enough to keep about 3
> full-dumps worth of compressed 
> data, but even a single uncompressed full dump would
> not fit...
> 	-mi

 I'm not sure if this will help you but long ago there
was a problem with reads and writes being too fast and
we used to use a mount option to slow things down to

 server:/dir/dir  /localdir/mountme  nfs rw,-w=1024

 #man mount_nfs
 sets the write data size to the specified value...

 Again not sure if this will help but thought I would
suggest it.


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