Date: Wed, 11 Jan 2012 01:04:59 -0500 From: "Mikhail T." <mi+thun@aldan.algebra.com> To: Bob Friesenhahn <bfriesen@simple.dallas.tx.us> Cc: fs@freebsd.org Subject: Re: How to best send files over network? Message-ID: <4F0D268B.9060908@aldan.algebra.com> In-Reply-To: <alpine.GSO.2.01.1201101741080.20764@freddy.simplesystems.org> References: <4F0CBB79.7010704@aldan.algebra.com> <alpine.GSO.2.01.1201101741080.20764@freddy.simplesystems.org>
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On 10.01.2012 18:49, Bob Friesenhahn wrote:
> 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
> multiple thereof.
Well, that was the reason cited for not using sendfile over ZFS. But
mmap/write, it was claimed, was efficient.
What's the general opinion of using mmap/write, when the file is on UFS?
Is it just as good as sendfile, or can sendfile be better under some
circumstances?
> 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).
No, thanks. I'm certainly not doing a read/write loop -- that's just too
disgusting in the age of better interfaces (even if those aren't well
implemented yet) :-)
>
>> 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 example?
>
> Use it to obtain the filesystem block size.
Ok, but still -- how does one determine the filesystem, where a
particular file resides? Thanks!
-mi
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