LVM negates benefits of jounaling filesystems? [was RFE: autofsck]

[Eric Sandeen]

Alan Cox wrote:
> On Tue, Jun 10, 2008 at 09:49:16AM -0500, Eric Sandeen wrote:
>>         if (unlikely(bio_barrier(bio))) {
>>                 bio_endio(bio, -EOPNOTSUPP);
>>                 return 0;
>>         }
>>
>> ... and somebody should probably measure the lvm overhead in general, I
>> suppose.  :)
> 
> About 30% for disk performance on my test box. Obviously that isn't all
> some LVM code corner case and there are other problems in there to reach
> that difference on dbench. That's FC8 and I believe some lvm fixes for
> performance have occurred since I did the runs (FC8 no updates).
> 
> Alan
> 

quick test; fast hardware raid on fibrechannel, 4 cpu opteron, 8G
memory, 4-threaded dbench for 600s, 120s warmup, 500G ext3 fs, 2.6.26-rc2.

ext3 on /dev/sdc:
Throughput 679.495 MB/sec 4 procs

ext3 on /dev/mapper/myvg-lvol0 on /dev/sdc:
Throughput 665.599 MB/sec 4 procs

-Eric