Strange hardware problem, any clue is welcome
I have a really strange problem with an computer from this fruit company
in my family:
It's an iMac from 2008, still running osx 10.6, but I put Testing on it
several months ago as the second OS (which is much better, as I
think...). Therefore I shrinked the existing partition on the 500GB SATA
hard drive and added a small boot partition and an ext4 partition for /.
The system was fully encrypted.
Unfortunately, there was a problem with disk I/O: booting into Linux
went well, sometimes the machine worked normal, but most of the time it
got very slow after some time (maybe after about an hour, sometimes
earlier, sometimes never) during disk activity. It was very difficult to
work with. After a warm reboot the firmware didn't find any disk most of
the time but not always.
Last week I replaced Testing by osx 10.10. The installation went well
and it seemed that everything works. About an hour later I discovered
the possiblity to enable disk encryption; what happens is that the OS
sets a kind of partition flag and starts encrypting the partition on the
fly, one can continue to work! - one can even shutdown the system and
continue later. During this encryption process, the machine started
hanging again and later it was completely stuck. After a forced reboot,
it continued to encrypt but after a few minutes it's again stuck. This
seems to be reproducable every time I reboot, so the machine is just
unusable, the encryption is stuck at about two thirds. osx
10.6 didn't show these problems when it was used (without any
encryption), even in the last couple of
months, when Linux was already installed and showed the problems.
Now my question is: What can be the reason for this kind of problems?
A problem with the SATA controller? Than I would expect the problems
with each OS, including 10.6, which doesn't seem to be the case. Same is
true for a damaged SATA cable.
A problem with certain sectors on the disk? Than I would expect many I/O
errors, but this is not the case: SMART showed no problems at all, Linux
worked sometimes but it got very slow (disk access rates of a few kb/s),
now 10.10
gets r/w rates exactly equal to 0!
Might it be related to the encryption? But why, does it change the disk
access patterns in some way?
Every idea what's going on is very welcome!
PS: The computer is not used for serious work anymore, all data is moved
to a nice new machine running Testing
very well; it's just out of curiosity, I don't like not understanding
what's going on ;-)
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