[Gluster-users] Gluster caching behaviour

[Eliezer Croitoru]

Hey Marcus,

The first thing I would try is:
https://www.kernel.org/doc/Documentation/sysctl/vm.txt

It's the basic docs that describes the function by itself and it's 
technical idea.
Once you know the function idea you might understand a bit more about 
why to choose one value over the other.
For example "vm.swapiness" as "0" is nice but there is a reason that the 
swap actually happen.
The main issue with it is that there was a usage for above a specific 
amount of memory on the system.
You would feel the "slow" speed of the service and then understand that 
it is using more swap that it needs and understand that the service 
works utilizing lots of ram which the system was designed to not use always.
A really good design should results in a system that is not utilizing 
100% of it's RAM by default.
When the ram is used by 100% and you need to check your options you 
cannot even consider running a simple "ls" since this will cause the 
system to get stuck if the DISK has high I/O rate.

You can say that all the defaults are kind of designed to let the system 
to stay stable enough to allow Start it UP.

On cases you do know the size of the system I would tune them if I 
understand the meaning of them to prevent real damage and to first allow 
me breath some air before diving into any decision regarding a big system.

All The Bests,
Eliezer

On 03/12/13 13:04, Marcus Bointon wrote:
> On 3 Dec 2013, at 06:13, Robert Hajime Lanning <lanning at lanning.cc> wrote:
>
>> I have these tuned for my system:
>> vm.swappiness
>> vm.vfs_cache_pressure
>> vm.dirty_background_ratio
>> vm.dirty_ratio
>> vm.dirty_writeback_centisecs
>> vm.dirty_expire_centisecs
>>
>> This pretty much goes for any storage server that is filesystem based (ext2/3/4,xfs,btrfs,zfs...)
>>
>> Very important to tune these values when you have large amounts of RAM.
>
> Do you happen to have any good guides on tuning those? I've only encountered swappiness before.
>
> Marcus
>
>
>
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