High la but everything flies, how is it?

Question

linux

Tell me the people, the situation is as follows:
Server on a processor with 4 cores.
It costs centos 6.5
NGINX + Apache
Raised software RAID 0
LA today it has become an average of 6.7
percent loaded on 2%
wa 4-12%
of 16 GB RAM, half is occupied.
All sites run fast.
Excites such a high LA. (Usually, it doesn’t rise above 2.0.
What could it be?
Pysy
I sin on the raid.

Answer 1

LA is, roughly, the number of processes in the former state R (and not only in it, for example, the status D also matters) per unit of time. Those. if you have several sluggish processes that do not load the physical subsystems of the server, but at the same time cannot be completed quickly, for example, due to slow data flow over the network, then LA is high, although in fact the physical resources of the server will not be outside. But this is not exactly and not entirely true, it is rude. And based on this situation, LA can be high, but useful requests are processed quickly, because. Indeed, the resources are there.
As Ian said, LA 0.8-1 per core is considered normal. But in any case, if there is no reason for the load, i.e. a normal (i.e., optimized, not heavy) site is visited by a couple of three people a day, high LA is not normal and you are rightly puzzled.
Here I can advise you to start looking through top, htop processes in the R and D status, as I already mentioned, and having found such, look through strace and lsof, what they are doing and where they are breaking. This is the simplest, but often helps.
Plus, atop with the -r option in the mode via the p button can also help (it seems that it should be responsible for the total number of processes involved in the measurement interval, by default 10 minutes), because suddenly the processes start and end quickly, faster than in the update interval top/ htop (especially since your wa is small). It is worth noting that in 5 and 6 centos, atop as a daemon is not automatically started after installation and is not added to autorun. I don't know about the seventh.
Well, in general, yes, it’s like treating a disease from a photograph, nothing can be said without viewing the server itself. But start with the above, it will suddenly lead to a sensible thought.