On Sat, Apr 18, 2009 at 05:25:17PM -0500, Bob Friesenhahn wrote: > On Sat, 18 Apr 2009, Gary Mills wrote: > > >How do we determine which layer is responsible for the slow > >performance? > > If the ARC size is diminishing under heavy load then there must be > excessive pressure for memory from the kernel or applications. A 30GB > ARC is quite large. The slowdown likely increases the amount of RAM > needed since more simultaneous requests are taking place at once and > not completing as quickly as they should. Once the problem starts, it > makes itself worse.
It was diminishing under load when the server had only 16 GB of memory. There certainly was pressure then, so much so that the server became unresponsive. Once we upgraded that to 64 GB, the ARC size stayed high. I gather then that there's no longer pressure for memory by any of the components that might need it. > It is good to make sure that the backup software is not the initial > cause of the cascade effect. The backup is also very slow, often running for 24 hours. Since it's spending most of its time reading files, I assume that it must be cycling a cache someplace. I don't know if it's suffering from the same performance problem or if it's interfering with the IMAP service. Certainly, killing the backup doesn't seem to provide any relief. I don't like the idea of backups running in the daytime, but I get overruled in that one. -- -Gary Mills- -Unix Support- -U of M Academic Computing and Networking- _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
