linux-ext4 - Re: Porting Zfs features to ext2/3

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Message-ID:  <loom.20080729T222131-137@post.gmane.org>
Date:	Tue, 29 Jul 2008 22:52:26 +0000 (UTC)
From:	Szabolcs Szakacsits <szaka@...s-3g.org>
To:	linux-ext4@...r.kernel.org
Subject:  Re: Porting Zfs features to ext2/3

Theodore Tso <tytso <at> mit.edu> writes:
> On Sun, Jul 27, 2008 at 04:54:41PM -0600, Eric Anopolsky wrote:
> > On Sun, 2008-07-27 at 01:49 -0700, postrishi wrote:
> > > 
> > > I want to know that has any work been done to port the Zfs features to
> > > ext2/3
> > 
> > Did you know that ZFS is available for Linux?
> 
> ZFS is available in a FUSE filesystem.  As a userspace filesystem, it
> means a huge number of context switches to get data between the disk,
> to the kernel, to the FUSE userspace, back to the kernel, and to the
> process trying to access the ZFS file.  

Transferring 4 kB from a commodity disk (disk seek + rotational delay + 
transfer) takes usually between 100-4,000 usec. Two context switches 
take about 2 usec, i.e. only 2-0.05% of the full data transfer time. 

In other words, there isn't really time for huge number of context 
switches because most of the time is spent waiting for the disk.

> That's not going to be high performance.  

I did also an in memory test on a T9300@2.5, with disk I/O completely 
eliminated. Results:

tmpfs:    975 MB/sec
ntfs-3g:  889 MB/sec  (note, this FUSE driver is not optimized yet)
ext3:     675 MB/sec

> For someone who wants to migrate from Solaris to Linux,
> it might be useful, but I'm not sure you would really want to use a
> ZFS/FUSE implementation in production.

It seems the problem is that the only active ZFS-FUSE developer was 
hired by SUN and since then not much (visible) is happening.

Regards,  Szaka

--
NTFS-3G: http://ntfs-3g.org



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