Hello Andreas,
Thank you for your fast reply!
We use this setup for our backup servers.
We use rsync via SSH using hard links as backup technology; the backup
server is pulling the data from several servers.
The setup is 12x1TB disks in RAID6 128k stripe, using ext3 4k block +
lvm2 with the journal on Gigabyte I-RAM drive 1GB DDR400.
The server has 8GB RAM.
The journal mode is data.
The journal size is 400MB.
When we moved the journal on the external device we have gained like 20%
performance improvement with our backup.
I'm converting several servers to ext4 to see what will be the
performance improvement for our workload.
Do you have any suggestions regarding the journal size and the overall
file system setup?
Thank you again!
Iavor
Andreas Dilger wrote:
On 2009-12-07, at 14:46, Iavor Stoev wrote:
I wonder if the Ext3's MAX journal size of 102,400 file system blocks
has been increased in Ext4.
I'm using 10TB 4k block Ext3 file system with external journal on
Gigabyte I-Ram drive and I'm planning a migration to Ext4 system.
And I wonder if I can increase the journal size over 400MB.
Well, even with ext3 the maximum journal size was only for internal
journals. It was always possible to have larger external journal devices.
With ext4, the maximum journal size WAS increased, though this is in
fact a mke2fs/tune2fs limit so it is also increased for new ext3
filesystems.
Note that with large journals you are also consuming an equal amount of
RAM as the size of the journal, so don't make it crazy big. Having a
journal on SSD is only really noticable for sync-happy workloads. It
isn't noticably better than using a regular disk for the external
journal if you aren't doing a lot of syncs (e.g. NFS or email).
I've thought in the past that it might be an interesting hack to use a
huge journal device (say 32GB) with data journaling, and then have the
JBD layer get the data blocks from the journal for checkpointing to the
filesystem instead of keeping the buffers pinned in RAM. That would
would allow blazing metadata workloads, zero seeking, and then
checkpointing in bulk to the filesystem. ... but unfortunately not
something I have time to test out.
Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.
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