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

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Date:	Thu, 07 Aug 2008 14:09:35 +0200
From:	Goswin von Brederlow <goswin-v-b@....de>
To:	Theodore Tso <tytso@....EDU>
Cc:	Szabolcs Szakacsits <szaka@...s-3g.org>, linux-ext4@...r.kernel.org
Subject: Re: Porting Zfs features to ext2/3

Theodore Tso <tytso@....EDU> writes:

> On Tue, Jul 29, 2008 at 10:52:26PM +0000, Szabolcs Szakacsits wrote:
>> 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
...
> So it's issueing lots of 4k writes, one page at a time, because it
> needs to track the completion of each block.  This creates a
> significant CPU overhead, which dominates in an all-memory test.
> Although this is not an issue in real-life today, it will likely
> become an issue in real-life solid state disks (SSD's).

This already is a major issue for us. We are starting to use SAS raid boxes
that deliver >350MB/s write and >600MB/s read performance with lustre,
which is ext3 with patches. It is somewhat between ext3 and ext4 in
that it has some of its features but not all.

> Fortunately, ext4's blktrace when copying a large file looks like
> this:

That is promising. Once the 64BIT feature becomes usable we plan to
port lustre to use ext4 as base filesystem. The current 8TiB limit is
a real pain.

MfG
        Goswin
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