Re: Debugging system freezes on filesystem writes

From: Marcus Sundman
Date: Tue Feb 26 2013 - 13:41:56 EST

On 24.02.2013 03:20, Theodore Ts'o wrote:
On Sun, Feb 24, 2013 at 11:12:22AM +1100, Dave Chinner wrote:
/dev/sda6 /home ext4 rw,noatime,discard 0 0
I'd say that's your problem....
Looks like the Sandisk U100 is a good SSD for me to put on my personal
"avoid" list:

There are a number of SSD's which do not implement "trim" efficiently,
so these days, the recommended way to use trim is to run the "fstrim"
command out of crontab.

OK. Removing 'discard' made it much better (the 60-600 second freezes are now 1-50 second freezes), but it's still at least an order of magnitude worse than a normal HD. When writing, that is -- reading is very fast (when there's no writing going on).

So, after reading up a bit on this trimming I'm thinking maybe my filesystem's block sizes don't match up with my SSD's blocks (or whatever its write unit is called). Then writing a FS block would always write to multiple SSD blocks, causing multiple read-erase-write sequences, right? So how can I check this, and how can I make the FS blocks match the SSD blocks?

Best regards,

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