Hi, I in no way pretend to know a lot about the kernel and the specific ways it handles free memory and caches, but i just look at it from a "logical" point of view.
Hopefully I'm not too far off course in the assumptions i make! Hope Rik can clarify this not just for me but for everyone thats been following this thread. Since he is the expert on this, he's the authority! Sincerely, Jason ----- Original Message ----- From: "Russell Coker" <[EMAIL PROTECTED]> To: "Jason Lim" <[EMAIL PROTECTED]> Cc: <debian-isp@lists.debian.org>; <[EMAIL PROTECTED]> Sent: Monday, June 11, 2001 6:43 PM Subject: Re: Finding the Bottleneck On Saturday 09 June 2001 20:04, Jason Lim wrote: > I'm not exactly sure how the Linux kernel would handle this. > > Right now, the swap is untouched. If the server needed more ram, > wouldn't it be swapping something... anything? I mean, it currently has > 0kb in swap, and still has free memory. That is a really good point. What you say makes a lot of sense. However the Linux kernel policies on when to free cache and when to swap are always being tweaked and are very complex. I have CC'd this message to Rik. Rik wrote most of the code in question and is the expert in this area. Rik, as a general rule if a machine has 0 swap in use then can it be assumed that the gain from adding more RAM will be minimal or non-existant? Or is my previous assumption correct in that it could still be able to productively use more RAM for cache? As a more specific issue, assuming that there is memory which is not being touched (there always is some) will that memory ever be paged out to allow for more caching? I believe that Jason is using kernel 2.2.19, but I would like to have this issue clarified for both 2.2.19 and 2.4.5 kernels if possible. > Anyway... as for the raid solution, is there anything I should look out > for BEFORE i start implementing it? Like any particular disk or ext2 > settings that would benefit the mail queue in any way? Don't want to > get everything set up, only to find I missed something critical that > you already thought of! There is an option to mke2fs to tune it for RAID-0 or RAID-5. I'm not sure if it provides much benefit though, and it does not help RAID-1 (which is the RAID level you are most likely to use). I suggest that you firstly run zcav from my bonnie++ suite on your new hard drives. Then allocate partitions for the most speed critical data in the fastest parts of the drives. Then use RAID-1 on those partitions. Good luck! -- http://www.coker.com.au/bonnie++/ Bonnie++ hard drive benchmark http://www.coker.com.au/postal/ Postal SMTP/POP benchmark http://www.coker.com.au/projects.html Projects I am working on http://www.coker.com.au/~russell/ My home page
