An active RHEL system should be using almost all of the free physical memory for cache and buffers. Once you start doing application I/O, you'll see the memory get "used" by the OS quickly. Remember, the memory "used" for cache/buffers is actually free and the kernel can reclaim it very quickly if memory demand for processes increases. The "free" command shows you the difference between "used" memory with and without including the cache/buffers.
Older versions of Linux did have a penalty for very large memory because the algorithms used to manage memory pages were primitive. Many of those problems were addressed in later RHEL 4 releases and by the time we got to RHEL 5 and 6, those issues have been completely resolved. Many of our servers run 256 or 512GB of RAM. For a BL460c with maybe 8 cores, 32GB seems to me to be about right. If it's a BL460cG6 with 16 cores, 32GB seems small. It all depends on what applications or databases you're running on it.
Here's an example from a mid range system with 48 cores:
At first glance it looks like this system has no free memory. But the actual memory used by processes is actually only 24GB - the other 226GB is cache/buffers.
With very large amounts of RAM on certain hardware you can encounter NUMA issues, but as a general rule, you can never have too much memory. RHEL will find a way to use it.
Any penalty usually associated with having more memory is offset by having... more memory. Memory is faster than disk. This saves swapping operations.
The things to look out for are not as much with the memory, but the address tables. If your application supports hugepages then you might want to enable them for a sub section of your RAM to lower the footprint of your memory table.
Also,
This is more of an issue on intel systems than AMD, but you should make sure that your memory is aligned more properly. With intel systems, if you were to increase the memory you are more likely to run into issues where the speed of the RAM decreases (clock speed) or that you run memory in non-optimal channels (three channel vs dual channel).
Hi,
kstat -p -m zfs -n arcstats -s size returns
zfs:0:arcstats:size 8177310584
this values is approx (7.61 GB)
but my Physical Memory size is only 6144 Megabytes.
Can this happen ?
if yes, then how can I find free memory on the system.
BTW, I ran the kstat commands from a Non... (2 Replies)
Hi,
I am new to unix. I am working on Red Hat Linux and side by side on AIX also. After reading the concepts of Storage, I am now really confused regarding the terminologies
1)Physical Volume
2)Volume Group
3)Logical Volume
4)Physical Partition
Please help me to understand these concepts. (6 Replies)
After a memory upgrade all network interfaces are misconfigued. How do i resolve this issue. Below are some out puts.thanks.
ifconfig: plumb: SIOCLIFADDIF: eg000g0:2: no such interface
# ifconfig eg1000g0:2 plumb
ifconfig: plumb: SIOCLIFADDIF: eg1000g0:2: no such interface
# ifconfig... (2 Replies)
I have a Sun T5120, and I want to programmatically determine how much RAM it has.
# uname -a
SunOS myhost 5.10 Generic_141444-09 sun4v sparc SUNW,SPARC-Enterprise-T5120
The box has 64Gb; I tried prtdiag and prtconf, but they give me bogus info
prtconf gives me:
# prtconf |grep -i... (12 Replies)
Hello All,
Can anybody please tell me what is the maximum limit of Physical IBM Power Machine which can be handled by single HMC at a single point of time?
Thanks,
Jenish (1 Reply)
Hi All,
I am trying to find the physical memory usage by each process/users.
Can you please let me know how to get the memory usage?.
Thanks,
bsraj. (12 Replies)
I was in smit, checking on disc space, etc. and it appears that one of our physical volumes that is part of a large volume group, has no free physical partitions. The server is running AIX 5.1. What would be the advisable step to take in this instance? (9 Replies)
Hello,
I need explanations about physical disks and physical volumes. What is the difference between these 2 things?
In fact, i am trying to understand what the AIX lspv2command does.
Thank you in advance. (2 Replies)