-----Original Message----- From: fedora-list-bounces@xxxxxxxxxx [mailto:fedora-list-bounces@xxxxxxxxxx]On Behalf Of Matthew Miller Sent: Tuesday, January 18, 2005 9:52 AM To: For users of Fedora Core releases Subject: Re: long writes On Tue, Jan 18, 2005 at 09:44:09AM -0800, Brian Stark wrote: > I'm not sure if this is the proper forum, but it seems like a good place > to start. I am maintaining a linux cluster of servers (to date around > 350). They have a partition configured as a RAID, the average performance > on these servers is very good , but occasionally I will see a server go > away for 30-40 seconds. After researching it in the code I found that the > culprit was a "write" function call. When the call eventually completes, > but I am writing under 100K of data so I have no idea why it would take > that long to complete. Has anyone else seen this type of behavior? If not Which IO scheduler are you using? -- Matthew Miller mattdm@xxxxxxxxxx <http://www.mattdm.org/> Boston University Linux ------> <http://linux.bu.edu/> Thanks for the reply, We are configured to use the deadline IO scheduling algorithm, we made this decision after finding a similar issue on the read side. Even with deadline our worst case on the write seems to be much worse then the read side, an outrageous 30-40 seconds. Our servers may be under a significant load both in memory usage and CPU, what I am mostly interested in is an explanation. If its something we have to live with we will work around it, but if we are doing something stupid I would rather fix it. below is the code snippet we use to open the file: oflags = O_NDELAY; oflags |= O_WRONLY; /* only writing is permitted */ oflags |= O_CREAT; /* create the file if it doesn't exist */ oflags |= O_TRUNC; /* truncate the file if it does exist */ oflags |= O_NONBLOCK; /* do not block on reads and writes this will provide us with asynchronous behavior*/ fd = open(fn, oflags, 0666); The only thing that strikes me are the O_NDELAY and O_NONBLOCK flags. I understand (now) that writes to disk will block despite these flags, but will their usage also cause any odd behavior, or am I grasping at straws. Brian -- fedora-list mailing list fedora-list@xxxxxxxxxx To unsubscribe: http://www.redhat.com/mailman/listinfo/fedora-list
