On Tue, Feb 26, 2013 at 1:57 PM, Kevin Decherf <kevin@xxxxxxxxxxxx> wrote:
> On Tue, Feb 26, 2013 at 12:26:17PM -0800, Gregory Farnum wrote:
>> On Tue, Feb 26, 2013 at 11:58 AM, Kevin Decherf <kevin@xxxxxxxxxxxx> wrote:
>> > We have one folder per application (php, java, ruby). Every application has
>> > small (<1M) files. The folder is mounted by only one client by default.
>> >
>> > In case of overload, another clients spawn to mount the same folder and
>> > access the same files.
>> >
>> > In the following test, only one client was used to serve the
>> > application (a website using wordpress).
>> >
>> > I made the test with strace to see the time of each IO request (strace -T
>> > -e trace=file) and I noticed the same pattern:
>> >
>> > ...
>> > [pid 4378] stat("/data/wp-includes/user.php", {st_mode=S_IFREG|0750, st_size=28622, ...}) = 0 <0.033409>
>> > [pid 4378] lstat("/data/wp-includes/user.php", {st_mode=S_IFREG|0750, st_size=28622, ...}) = 0 <0.081642>
>> > [pid 4378] open("/data/wp-includes/user.php", O_RDONLY) = 5 <0.041138>
>> > [pid 4378] stat("/data/wp-includes/meta.php", {st_mode=S_IFREG|0750, st_size=10896, ...}) = 0 <0.082303>
>> > [pid 4378] lstat("/data/wp-includes/meta.php", {st_mode=S_IFREG|0750, st_size=10896, ...}) = 0 <0.004090>
>> > [pid 4378] open("/data/wp-includes/meta.php", O_RDONLY) = 5 <0.081929>
>> > ...
>> >
>> > ~250 files were accessed for only one request (thanks Wordpress.).
>>
>> Okay, that is slower than I'd expect, even for an across-the-wire request...
>>
>> > The fs is mounted with these options: rw,noatime,name=<hidden>,secret=<hidden>,nodcache.
>>
>> What kernel and why are you using nodcache?
>
> We use kernel 3.7.0. nodcache is enabled by default (we only specify user and
> secretfile as mount options) and I didn't find it in the documentation of
> mount.ceph.
>
>> Did you have problems
>> without that mount option? That's forcing an MDS access for most
>> operations, rather than using local data.
>
> Good question, I will try it (-o dcache?).
Oh right — I forgot Sage had enabled that by default; I don't recall
how necessary it is. (Sage?)
>> > I have a debug (debug_mds=20) log of the active mds during this test if you want.
>>
>> Yeah, can you post it somewhere?
>
> Upload in progress :-)
Looking forward to it. ;)
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