Theodore Tso <tytso@xxxxxxx> writes:
> On Tue, Jul 29, 2008 at 10:52:26PM +0000, Szabolcs Szakacsits wrote:
>> I did also an in memory test on a T9300@xxx, 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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