How to best send files over network?
bfriesen at simple.dallas.tx.us
Wed Jan 11 00:01:47 UTC 2012
On Tue, 10 Jan 2012, Mikhail T. wrote:
> I'm trying to implement a BSD-tuned sending of files. Most of the files are
> fairly large. I thought, sendfile(2) is the way to go, but, it seems, there
> are severe performance problems at the moment for the files located on a ZFS.
> mmap-ing the files and then write-ing them is claimed to be a lot faster.
> Could somebody comment on this? Should one always mmap/write, or are there
> situations, when sendfile is advantageous?
Don't use mmap on zfs since doing so wastes memory (zfs ARC is not
coherent with mmap page cache). Instead do normal file I/O (e.g.
write, fwrite) using the filesystem blocksize (e.g. 128K) or a small
Of course if you are doing this over the network then you will need a
program on the receiving end to write the data, and a program on the
sending end to send it.
It is useful to cache several blocks on the receiving end and use a
thread to receive data from the network in case zfs temporarily stalls
during write (which it periodically does).
> If, indeed, sendfile is best for UFS, but mmap/write is better over ZFS, what
> is the best way to determine the underlying FS for each file? statfs(2) is
> supposed to answer that question -- what should I look for in the struct
> statfs, that it will return? Do I check, if f_fsid contains a magic number
> for ZFS, or look for a magic string in f_fstypename? Could someone provide an
Use it to obtain the filesystem block size.
> Thank you very much. Yours,
Good to hear from you!
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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