throttling NFS writes
mi+mx at aldan.algebra.com
Sat Nov 19 00:24:46 GMT 2005
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
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
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
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...
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