This issue has been discussed a number of times in this forum. To summerize:
ZFS (specifically, the ARC) will try to use *most* of the systems available memory to cache file system data. The default is to max out at physmem-1GB (i.e., use all of physical memory except for 1GB). In the face of memory pressure, the ARC will "give up" memory, however there are some situations where we are unable to free up memory fast enough for an application that needs it (see example in the HELIOS note below). In these situations, it may be necessary to lower the ARCs maximum memory footprint, so that there is a larger amount of memory immediately available for applications. This is particularly relevant in situations where there is a known amount of memory that will always be required for use by some application (databases often fall into this category). The tradeoff here is that the ARC will not be able to cache as much file system data, and that could impact performance. For example, if you know that an application will need 5GB on a 36GB machine, you could set the arc maximum to 30GB (0x780000000). In ZFS on on10 prior to update 4, you can only change the arc max size via explicit actions with mdb(1): # mdb -kw > arc::print -a c_max <address> c_max = <current-max> > <address>/Z <new-max> In the current opensolaris nevada bits, and in s10u4, you can use the system variable 'zfs_arc_max' to set the maximum arc size. Just set this in /etc/system. -Mark Erik Vanden Meersch wrote:
Could someone please provide comments or solution for this? Subject: Solaris 10 ZFS problems with database applications HELIOS TechInfo #106 ==================== Tue, 20 Feb 2007 Solaris 10 ZFS problems with database applications -------------------------------------------------- We have tested Solaris 10 release 11/06 with ZFS without any problems using all HELIOS UB based products, including very high load tests. However we learned from customers that some database solutions (known are Sybase and Oracle), when allocating a large amount of memory may slow down or even freeze the system for up to a minute. This can result in RPC timeout messages and service interrupts for HELIOS processes. ZFS is basically using most memory for file caching. Freeing this ZFS memory for the database memory allocation can result into serious delays. This does not occur when using HELIOS products only. HELIOS tested system was using 4GB memory. Customer production machine was using 16GB memory. Contact your SUN representative how to limit the ZFS cache and what else to consider using ZFS in your workflow. Check also with your application vendor for recommendations using ZFS with their applications. Best regards, HELIOS Support HELIOS Software GmbH Steinriede 3 30827 Garbsen (Hannover) Germany Phone: +49 5131 709320 FAX: +49 5131 709325 http://www.helios.de -- <http://www.sun.com/solaris> * Erik Vanden Meersch * Solution Architect *Sun Microsystems, Inc.* Phone x48835/+32-2-704 8835 Mobile 0479/95 05 98 Email [EMAIL PROTECTED] ------------------------------------------------------------------------ _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
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