After a recent PHP ugprade to 5.3 (which is meanwhile EOL, too), the system load sharply increased, mainly due to very high disk i/o:
I got aware that there were many write operations right after the upgrade:
I used iotop to see what process is reponsible for it, unfortunately it was always the kjournald process - not a big help actually. I suspected eAccelerator as the reason because now all the cached php scripts needed to be rewritten for the new PHP 5.3 code. But the load was still way too high, even after half an hour.
At the same time I started testing some of the websites on that server. On one of them I got an error message:
PHP Warning: Unknown: open_basedir restriction in effect. File() is not within the allowed path(s):
As soon as I saw that, I remembered, that I have already once had that issue and even wrote an article about that: Upgraded to PHP 5.3: Suddenly open_basedir restriction warnings appear.
So I recompiled eAccelerator with the necessary configure option (--without-eaccelerator-use-inode) and restarted Apache. A few minutes later, the load dropped to its normal average value.