Bernd Schubert wrote:
On Tuesday 15 July 2008 15:16:33 Ric Wheeler wrote:
Goswin von Brederlow wrote:
Theodore Tso <tytso@xxxxxxx> writes:
On Mon, Jul 14, 2008 at 09:50:56PM +0200, Goswin von Brederlow wrote:
I found ext4 64bit patches for e2fsprogs 1.39 that fix at least
mkfs. Does anyone know if there is an updated patch set for 1.41
anywhere? And when will that be added to e2fsprogs upstream?
Yes, this is correct. The 1.39 64-bit patches break the shared
library ABI, and also there were some long-term problems with having
super-large bitmaps taking huge amounts of memory without some kind of
run-length encoding or other compression technique. I decided to
reject the 1.39 approach because it would have caused short- and
long-term maintenance issues.
Is that a problem for the kernel or for the user space? I notices that
mke2fs 1.39 used over a gigabyte memory to format a >16TiB disk. While
being a lot that is not really a problem here.
At the moment 1.41 does not support > 32 bit block numbers. The
priority was to get something which supported all of the other ext4
features out the door, since that would allow much better testing of
the ext4 code base. We are now working on 64-bit support in
e2fsprogs, with mke2fs coming first, and the other tools coming later.
But yeah, good quality 64-bit e2fsprogs support is going to lag for a
bit. Sorry, we're working as fast as we can, given the resources we
have.
Will there be filesystem changes as well? The above mentioned
run-length encoding sounds a bit like a new bitmap format or is that
only supposed to be the in memory format in userspace?
What is the plan of how to add 64-bit support to the shared lib now?
Will you introduce a do_foo64() function in parallel to do_foo() to
maintain abi compatibility? Will you add versioned symbols? Or will
there be an abi break at some point?
The reason I ask all this is because I'm willing to spend some time
patching and testing. A single >16TiB filesystem instead of multiple
smaller ones would be a great benefit for us.
Can you give us any details about your use case? Is it hundreds of very
large files, or 100 million little ones?
Depends on our customers. Though lustre is rather slow for small files and we
try to inform our customers about that. On the other hand there also also no
choices of cluster filesystem for small files.
Thanks - so this is not an internal application, but hosting for various
workloads? We have different scalability issues depending on the nature
and mix of file sizes, etc.
Any interesting hardware in the mix on the storage or server side?
What exactly do you want to know? Usually we have a server-pair and Infortrend
Raid-units. Since lustre doesn't do any redundancy on its own, we usually
also have a raid1, raid5 or raid6 of several raid units.
One thing that we have been working on/thinking about is how best to
automatically self tune a file system to the storage. Today, XFS is
probably the best normal linux file system at figuring out raid stripe
size, etc. Getting this enhanced in ext4 could lead to a significant
performance win for users who are not masters of performance tuning, etc.
How long would you wait for something like fsck to run to completion
before you would need to go to back up tapes? 6 hours? 1 day? 1 week ;-) ?
For ease of management and optimal performance, we need single partitions
larger than 8TiB (raid1) or 16TiB (raid5 or raid6). And the present 8TiB
limit strongly bites us.
Cheers,
Bernd
Makes sense, thanks for the information!
Regards,
Ric
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