Re: moving buffers/caching from RAM to SSD

2014-01-01 Thread Stan Hoeppner
On 1/1/2014 12:43 AM, Muhammad Yousuf Khan wrote:
 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.

Caching is used at many levels in computer systems, both in hardware,
the OS kernel, and in software applications.  But the implementations
are quite different.  Conceptually, Linux page caching and ZFS caching
may be similar, but they are quite different in implementation,
execution, and function.

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

Yes, a massive difference.

The DRAM bandwidth of a basic desktop system today w/dual channel
ddr3-1333 is ~20 GB/s.  The fastest SSDs are ~0.5 GB/s, or 40x slower.
The latency of modern DDR3 DRAM is ~50 ns (cache miss latency, not CAS
cycle time).  The latency of SSDs is ~100 μs, or 2000 times slower.

 Thanks all. i really appreciate your help.
 
 
 
 
 On Tue, Dec 31, 2013 at 10:33 PM, Stan Hoeppner s...@hardwarefreak.comwrote:
 
 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 sharedbuffers 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


 --
 To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org
 with a subject of unsubscribe. Trouble? Contact
 listmas...@lists.debian.org
 Archive: http://lists.debian.org/52c2ffeb.7010...@hardwarefreak.com


 


-- 
To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org 
with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org
Archive: http://lists.debian.org/52c42a1c.6060...@hardwarefreak.com



Re: moving buffers/caching from RAM to SSD

2013-12-31 Thread Muhammad Yousuf Khan
or an appropriate question would be . how can i use an SSD to boost the
system Performance.
i don't wanna store data on SSD however just wana use it for performance.




On Tue, Dec 31, 2013 at 6:54 PM, Muhammad Yousuf Khan sir...@gmail.comwrote:

 i dont know why i am saying is even practical or not.

 here is my free command

 @thor:# free -g
  total   used   free sharedbuffers 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.

 Thanks,
 Myk



Re: moving buffers/caching from RAM to SSD

2013-12-31 Thread Celejar
I'm probably missing something here, but why would you expect better
performance by moving cache from faster RAM to slower SSD?

On Tue, 31 Dec 2013 18:59:42 +0500
Muhammad Yousuf Khan sir...@gmail.com wrote:

 or an appropriate question would be . how can i use an SSD to boost the
 system Performance.
 i don't wanna store data on SSD however just wana use it for performance.
 
 
 
 
 On Tue, Dec 31, 2013 at 6:54 PM, Muhammad Yousuf Khan sir...@gmail.comwrote:
 
  i dont know why i am saying is even practical or not.
 
  here is my free command
 
  @thor:# free -g
   total   used   free sharedbuffers 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.
 
  Thanks,
  Myk
 


Celejar


-- 
To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org 
with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org
Archive: 
http://lists.debian.org/20131231092100.e679d949566b9e63c1e36...@gmail.com



Re: moving buffers/caching from RAM to SSD

2013-12-31 Thread Nemeth Gyorgy
2013-12-31 14:54 keltezéssel, Muhammad Yousuf Khan írta:
 i dont know why i am saying is even practical or not.
 
 here is my free command
 
 @thor:# free -g
  total   used   free sharedbuffers 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.

You shouldn't do it. Unused RAM is waste of RAM, and the memory is still
faster than the SSD, so if you manage to use the SSD for buffer instead
of RAM (which I don't think you can) your performance would be worse.


-- 
--- Friczy ---
'Death is not a bug, it's a feature'


-- 
To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org 
with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org
Archive: http://lists.debian.org/52c2d34e.7060...@freemail.hu



Re: moving buffers/caching from RAM to SSD

2013-12-31 Thread Stan Hoeppner
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 sharedbuffers 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


-- 
To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org 
with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org
Archive: http://lists.debian.org/52c2ffeb.7010...@hardwarefreak.com



Re: moving buffers/caching from RAM to SSD

2013-12-31 Thread Muhammad Yousuf Khan
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 s...@hardwarefreak.comwrote:

 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 sharedbuffers 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


 --
 To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org
 with a subject of unsubscribe. Trouble? Contact
 listmas...@lists.debian.org
 Archive: http://lists.debian.org/52c2ffeb.7010...@hardwarefreak.com