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HOWTO: Large File Copies over CIFS
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UberPinguin
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PostPosted: Thu Sep 27, 2007 2:55 am    Post subject: HOWTO: Large File Copies over CIFS Reply with quote

I work in a Windows Active Directory environment. Because of that, I deal with CIFS shares on a daily basis, and frequently have to copy very large files over the network (think hard drive backups in excess of 40 GB). If you've ever attempted this from a *nix box to a CIFS volume mounted with
Code:
# mount -o domain=somedomain,user=auser //windontserver/share /mnt/remote
you'll know that, partway through the copy, progress will slow to a crawl and eventually stop, with no errors reported. This is frustrating, to say the least. I have lost many hours of work to this situation.
Sifting through the mount(8) and mount.cifs(8) man pages, I came across the following:
mount.cifs(8):
directio
  Do  not  do inode data caching on files opened on this mount. This precludes mmaping files on this mount. In
  some cases with fast networks and little or no caching benefits on the client (e.g. when the application  is
  doing  large sequential reads bigger than page size without rereading the same data) this can provide better
  performance than the default behavior which caches reads (readahead) and writes  (writebehind)  through  the
  local  Linux  client  pagecache if oplock (caching token) is granted and held. Note that direct allows write
  operations larger than page size to be sent to the server. On some kernels this requires the cifs.ko  module
  to be built with the CIFS_EXPERIMENTAL configure option.
So, by changing the previous mount command to
Code:
# mount -o domain=somedomain,user=auser,directio //windontserver/share /mnt/remote
I gain improved performance for sequential read/writes. A brief test copying a 3.7GB bzipped tar file gave a consistent throughput of about 13-15 MB/s over a full-duplex 100Mb ethernet link from my laptop to the Windows 2003 server.
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You see, instead of arguing from ignorance, and fear, there is only one way to verify a theory. And that's not by clutching a black book and begging the sky fairy for deliverance from the mad scientists and their big machines.
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likewhoa
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Joined: 04 Oct 2006
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PostPosted: Thu Sep 27, 2007 2:29 pm    Post subject: Reply with quote

BOOKMARKED. thanks UberPinguin.
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daschapa
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Joined: 01 Sep 2006
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PostPosted: Fri Sep 28, 2007 1:29 am    Post subject: Reply with quote

You'll be saving many lives with this post. Thanx very much.
(Very much appreciated).your
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niceness
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Joined: 02 May 2006
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PostPosted: Fri Sep 28, 2007 10:09 am    Post subject: Reply with quote

This is one of the most useful tips I have come across in a long time.
Thanks :D
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UberPinguin
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PostPosted: Tue Oct 02, 2007 4:09 pm    Post subject: Reply with quote

No problem, glad I could help :D
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aidanjt wrote:
You see, instead of arguing from ignorance, and fear, there is only one way to verify a theory. And that's not by clutching a black book and begging the sky fairy for deliverance from the mad scientists and their big machines.
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