Re: moving buffers/caching from RAM to SSD

Thanks all, it was probably be my misunderstanding with both technologies (RAM and SSDs). i have been told that SSDs are fast enough like RAMs and to show the performance that person refer his OS boot time which was dramatically minimized.

i am also obsessed by the magic of ZFS. and ZFS people recommend using ZIL and logging on SSD. which apparently seems like the same process how linux cache things in RAM.

however with your help and searching on google i learn that there is a hell lot of difference in speed of RAM an SSD.

Thanks all. i really appreciate your help.

On Tue, Dec 31, 2013 at 10:33 PM, Stan Hoeppner <stan@hardwarefreak.com> wrote:

On 12/31/2013 7:54 AM, Muhammad Yousuf Khan wrote:
> i dont know why i am saying is even practical or not.
>
> here is my free command
>
> @thor:# free -g
> total used free shared buffers cached
> Mem: 31 31 0 0 0 26
> -/+ buffers/cache: 3 27
> Swap: 93 0 93
>
>
> as you can see 27GB is being used in caching. i have few 160GB SSDs.
> can i move this buffers/caching load to my SSD. so that things could work
> more better.

Muhammad,

By design, the Linux kernel will use nearly all free memory for caching
disk blocks and filesystem metadata when the memory isn't needed by
other processes.

When a process needs memory, the kernel simply drops some of the cached
pages, freeing them for immediate use. This process takes a few tens of
nanoseconds per 4KB page--it is instantaneous. It is because these
pages can be freed instantly that Linux eats up all the RAM for cache.
Cached file access is hundreds of times faster than disk access, even if
disk is SSD.

What you are seeing is the expected Linux kernel behavior. There is
nothing wrong here, nothing to fix.

--
Stan

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