On Mon, 2009-03-30 at 14:39 -0400, Mark Lord wrote:..Chris Mason wrote:I had some fun trying things with this, and I've been able to reliably..
trigger stalls in write cache of ~60 seconds on my seagate 500GB sata
drive. The worst I saw was 214 seconds.
I'd be more interested in how you managed that (above),
than the quite different test you describe below.
Yes, different, I think. The test below just times how long a single
chunk of data might stay in-drive cache under constant load,
rather than how long it takes to flush the drive cache on command.
Right?
Still, useful for other stuff.
That's right, it is testing for starvation in a single sector, not for
how long the cache flush actually takes. But, your remark from higher
up in the thread was this:
> > Anything in the drive's write cache very probably made > it to the media within a second or two of arriving there.
Sorry if I misread things. But the goal is just to show that it really..
does matter if we use a writeback cache with or without barriers. The
test has two datasets:
1) An area that is constantly overwritten sequentially
2) A single sector that stores a critical bit of data.
#1 is the filesystem log, #2 is the filesystem super. This isn't a
specialized workload ;)