Date: Fri, 18 Nov 2005 19:24:17 -0500 From: Mikhail Teterin <mi+mx@aldan.algebra.com> To: questions@freebsd.org Subject: throttling NFS writes Message-ID: <200511181924.17282.mi%2Bmx@aldan.algebra.com>
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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
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