Fedora 19 - filesystems slow

[Rick Stevens]

On 07/02/2014 11:36 AM, George R Goffe issued this missive:
> Rick,
>
> Thanks for your info. I'll check this out as well. I have used hdparm -B
> to get and set the APM values... All the drives including the system
> drive were set to 128. I have set them to 255 now so we'll see what happens.
>
> Actually, the behavior makes me think of a cache that has been
> emptied... My new activity has to rebuild the cache. Ideally, I'd like
> to make the cache bigger and have entries written back to the drive(s)
> BUT remain in cache... A least used algorithm could be used when looking
> for free space in the cache similar to the one for real memory. Do you
> know the developers or of a mailing list?

The filesystem cache is controlled by the kernel and the filesystem
modules. Part of RAM is reserved for caches and it's shared across all
the mounted filesystems IIRC. If a filesystem goes "inactive", then the
stuff cached for it will eventually be expired and that RAM will be
used for more active filesystems.

I don't know of a way to control either the size of the cache or its
retention period. It might be controllable via a sysctl, but I've never
tried to bugger things like that.

There are a number of resources about individual filesystems out there
on the web. Google your filesystem type and you should find some. For
example, http://ext4.wiki.kernel.org/index.php/Main_Page (for the ext4
filesystem).

> Again, thanks for your response.

No worries, mate. Glad I could help somewhat.

> ------------------------------------------------------------------------
> *From:* Rick Stevens <ricks at alldigital.com>
> *To:* George R Goffe <grgoffe at yahoo.com>; Community support for Fedora
> users <users at lists.fedoraproject.org>
> *Sent:* Wednesday, July 2, 2014 10:36 AM
> *Subject:* Re: Fedora 19 - filesystems slow
>
> On 07/02/2014 12:49 AM, George R Goffe issued this missive:
>
>
>
>  > Hi,
>  >
>  > I have a Fedora 19 system with several large 2-4TB drives attached
> via USB-SATA docking stations.
>  >
>  > I'm seeing a problem whereby a specific filesystem that hasn't been
> accessed for some time and is REALLY slow to respond to initial
> requests. ls -alt for example takes a substantial bit of time to respond
> at first but then response is acceptable after that.
>  >
>  > I'm trying to figure out what's happening and why and what I can do
> about it. It's like the buffers are empty and they need to be filled.
> Are there kernel tunable parameters that can be changed to avoid this
> problem?
>
>
> I can think of two things:
>
> 1) The drive was spun down because of inactivity. Try looking at the
> man page for "hdparm", specifically the "-B" and "-S" options.
>
> 2) Caching. If the filesystem hadn't been accessed in a while, its
> contents are probably no longer cached. Don't know if you can do
> anything about that.
> ----------------------------------------------------------------------
> - Rick Stevens, Systems Engineer, AllDigital ricks at alldigital.com
> <mailto:ricks at alldigital.com> -
> - AIM/Skype: therps2        ICQ: 22643734            Yahoo: origrps2 -
> -           -
> -              Careful!  Ugly strikes 9 out of 10 people!            -
>
> ----------------------------------------------------------------------
>
>


-- 
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- Rick Stevens, Systems Engineer, AllDigital    ricks at alldigital.com -
- AIM/Skype: therps2        ICQ: 22643734            Yahoo: origrps2 -
-                                                                    -
-       "As for me, I aspire to be the Walmart Greeter in Hell."     -
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