Slow disk write speeds over network
sean at chittenden.org
Wed Jun 11 13:55:51 PDT 2003
> > net.inet.tcp.sendspace=65536
> Double the default. Might not be a good idea, unless you have a ton
> of memory. You will potentially use 64K send + 64K receive times
> number of sockets. Assuming 4G and near-perfect tuning, you will be
> limited to 16384 simultaneous connections fully packed before memory
> pressure causes your machine to crash. I tend to like smaller
> buffers and more connections. If you only have 512M, drop this
> number to 2048 simultaneous connections if all buffers are full.
4GB of memory in this box and it's not directly available to the
Internet: a very important point to take into note when tuning.
> > kern.maxfiles=65536
> Seems kind of overkill for the number of connections you can support
> without overcommit, and the number of client machines you say you
This machine has a busy database on it too. :)
> > net.inet.udp.recvspace=65536
> > net.inet.udp.maxdgram=57344
> These are important for UDP NFS. I do not reccomend it.
Other than I do use UDP NFS, so I do recommend these values. :) The
relevance of the UDP vs TCP NFS should be kept to the archives, we
don't need to re-open that bikeshed. :)
> > vfs.nfs.async=1
> This is very dangerous, if you care about your data. It permits
> NFS to ACK writes before they have been committed to stable
> storage. With a large enough window size, this should not be
It's just as dangerous as write caching, same argument for/against
write caching, this is no worse.
> > net.inet.udp.log_in_vain=1
> This is just overhead; I reccomend turning it off.
Ehh.... there's something floating around someplace where I've been
getting errant NFS UDP packets and I haven't figured out what's going
on... this is useful for debugging in the absence of a firewall.
> > net.inet.icmp.icmplim=20000
> This is only useful for TCP; but it can be very useful. Basically,
> this is "connection rate limiting". If you have a ton of clients,
> or trying to "netbench" the system, then set this number up. For
> 100 NFS clients, it likely does not matter.
I beg to differ... any ideas on how you throttle UDP connections
without ICMP? A busy UDP NFS server will require this to be set
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