Occasional system hangups after upgrade to Lion: is it a disk or software problem? I have an 13 inch MacBook unibody Alu (early 2009, before they started to be called MacBook Pro) that I use every day for many hours (it's my work and life computer). Few weeks ago within few days I upgraded the RAM to 8Gb and the harddrive to Samsung 1TB HN-M101MBB (I cloned my old drive to the new one with SuperDuper). These were the first changes to the hardware (apart from new battery) I did from the original configuration. After using computer for few more days with Snow Leopard, I upgraded to Lion.

Since then, every week or so my computer freezes completely without apparent reason and no good explanation. I get notifications either that my harddrive was corrupted, or very cryptic message that (some application name, ie Mailplane or Papers) database was corrupted and it cannot write to disk "T" (I have no such drive). When I hard-reboot the computer, it can't find the home disk. When I reboot it again with option key and select recovery drive and run disk utility, it always reports that my home disk 'appears to be OK'. After another restart everything is back to normal again.

I have never had such problems before the Lion upgrade, but I am not sure if it's the software or the new harddrive. Any hint on what can be wrong and how to fix it would be greatly appreciated.

Thanks,
Yot
Nobody will tell you for sure (without diagnosing a problem), but you should definitely check both your harddrive and memory (corrupted memory may cause data loss while writing to HD. I had such a problem twice in my life.)

I prefere non-OS specific utilities:

SystemResqueCD
You can install it either on CD or on USB flash drive.
It contains a lot of diagnostic utils. One of them is memtest86+ which you can use to test you memory.

Memtest86+
It's is one of the most recognized software diagnostic tools on the planet. Since 2008 it supports Apple hardware. It checks memory by writing different binary patterns and checking what's actually stored in memory.



Red means bad

MHDD

Official site of this utility is dead, but you can find in here.
That's what you need to check your hard disk drive. I'm not sure that it will work on Apple hardware, but you can plug your hard drive in any PC or in external USB enclosure and check there.