Emulator stopping during mnesia writes

[Ulf Wiger]

On Wed, 10 May 2000, Klacke wrote:

>We at bluetail have had some serious troble with disk io too. In
>particular loads of disk operations that modify a directory entry 
>such as open/creat, unlink, rename
>
>What makes the situation a lot worse is that while disk io is
>pending, the emulator can't run no reductions at all and the overall 
>performance drops to an almost grinding halt.
>
>It also turns out that different file systems are better or worse.
>In particular FreeBSD with Soft updates performed well whereas
>UFS/Solaris and FFS/BSD performed bad (They are almost identical)

At AXD 301, we've also had some problems with disk I/O.
One of the things we uncovered was that Solaris likes to handle
/tmp as a virtual partition (unless you specify that you want it
to be a true disk partition). This can cause conflicts between
swapping and disk I/O to /tmp, which can lead to some magnificent
delays.

Another problem we've had is when testing an IDE drive, as a 
replacement for our current SCSI drives. Access times were 
significantly slower, and (I believe in combination with a few 
driver or HW bugs) could lead to whopping delays in disk access
-- which of course caused the whole VM to hang.

We've found ways around these problems, but would very much like 
to see a modification of the current I/O implementation.

BTW, in my own pet project - a web server for source code browsing 
in ClearCase, I've had great difficulty with the ClearCase client
sometimes causing delays of > 1 minute*. It's not a great feature
of a web server to get stuck for that long, servicing a single 
request. My solution was to create a number of slave nodes and 
spreading out the file requests to those nodes. This seems to 
work reasonably well (although I had to increase (!) net_ticktime
from 1 minute to 5 in order to keep the distribution going.)

* For those of you unfamiliar with ClearCase, the ClearCase client
hooks into the file I/O system, so if the ClearCase server is bogged
down, your file ops will hang.

/Uffe
-- 
Ulf Wiger, Chief Designer AXD 301         <ulf.wiger@REDACTED>
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