Messages in this thread |  | | From | John Alvord <> | Subject | Re: Zlatko's I/O slowdown status | Date | Fri, 02 Nov 2001 12:36:49 -0800 |
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On Fri, 2 Nov 2001 12:16:40 -0800 (PST), "Jeffrey W. Baker" <jwbaker@acm.org> wrote:
> > >On 2 Nov 2001, Zlatko Calusic wrote: > >> Andrea Arcangeli <andrea@suse.de> writes: >> >> > Hello Zlatko, >> > >> > I'm not sure how the email thread ended but I noticed different >> > unplugging of the I/O queues in mainline (mainline was a little more >> > overkill than -ac) and also wrong bdflush histeresis (pre-wakekup of >> > bdflush to avoid blocking if the write flood could be sustained by the >> > bandwith of the HD was missing for example). >> >> Thank God, today it is finally solved. Just two days ago, I was pretty >> sure that disk had started dying on me, and i didn't know of any >> solution for that. Today, while I was about to try your patch, I got >> another idea and finally pinpointed the problem. >> >> It was write caching. Somehow disk was running with write cache turned >> off and I was getting abysmal write performance. Then I found hdparm >> -W0 /proc/ide/hd* in /etc/init.d/umountfs which is ran during shutdown >> but I don't understand how it survived through reboots and restarts! >> And why only two of four disks, which I'm dealing with, got confused >> with the command. And finally I don't understand how I could still got >> full speed occassionaly. Weird! >> >> I would advise users of Debian unstable to comment that part, I'm sure >> it's useless on most if not all setups. You might be pleasantly >> surprised with performance gains (write speed doubles). > >That's great if you don't mind losing all of your data in a power outage! >What do you think happens if the software thinks data is committed to >permanent storage when in fact it in only in DRAM on the drive?
Sounds like switching write-caching off at shutdown is a valid way to get the data out of cache. But shouldn't it be switched back on again later?
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