[lustre-discuss] Small sequential reads on cached file are slow

Dilger, Andreas andreas.dilger at intel.com
Sun Oct 2 14:21:55 PDT 2016


Please test with Lustre master (pre-2.9.0). There were optimizations landed specifically to improve small file read performance.  While Lustre 2.9.0 isn't released yet, it is getting very close. 

Cheers, Andreas

> On Oct 2, 2016, at 06:54, Hans Henrik Happe <happe at nbi.ku.dk> wrote:
> 
> Hi,
> 
> While testing small sequential reads I noticed that Lustre is more than 10 times slower than local fs when reading cached data. So basically no network I/O to OSSes. I wanted to check if readahead was working for this small I/O case, but it seems that cached case isn't.
> 
> The client is running Lustre 2.8 and CentOS 6.8.
> 
> Lustre:
> 
> $ dd if=file of=/dev/null bs=512
> 2097152+0 records in
> 2097152+0 records out
> 1073741824 bytes (1.1 GB) copied, 20.5081 s, 52.4 MB/s
> 
> $ dd if=file of=/dev/null bs=4k
> 262144+0 records in
> 262144+0 records out
> 1073741824 bytes (1.1 GB) copied, 2.91177 s, 369 MB/s
> 
> $ dd if=file of=/dev/null bs=1M
> 1024+0 records in
> 1024+0 records out
> 1073741824 bytes (1.1 GB) copied, 0.160732 s, 6.7 GB/s
> 
> Local fs:
> 
> $ dd if=/tmp/file of=/dev/null bs=512
> 2097152+0 records in
> 2097152+0 records out
> 1073741824 bytes (1.1 GB) copied, 1.56432 s, 686 MB/s
> 
> $ dd if=/tmp/file of=/dev/null bs=4k
> 262144+0 records in
> 262144+0 records out
> 1073741824 bytes (1.1 GB) copied, 0.275451 s, 3.9 GB/s
> 
> $ dd if=/tmp/file of=/dev/null bs=1M
> 1024+0 records in
> 1024+0 records out
> 1073741824 bytes (1.1 GB) copied, 0.148798 s, 7.2 GB/s
> 
> 
> Is this a known issue?
> 
> Cheers,
> Hans Henrik Happe
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