If you have a SAN-attached storage array then the operating system does not know absolutely anything about underlying data structures and therefore it is useless for it to try being "smart" with an elaborate IO scheduler. For example you get one LUN from a storage array, which the system sees as one disk, but in fact it is a RAID5 array of 7 disks. It does not know where the data is placed so the IO scheduler cannot do much to optimise data access. Therefore the reasoning for using the noop scheduler is the same as inside the virtual machines. (virtual machines do not know how their data is physically stored either)
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Wednesday, October 21, 2009 11:29 AM To: Red Hat Enterprise Linux 5 (Tikanga) discussion mailing-list Subject: RE: [rhelv5-list] IO Scheduler and RAID HW or SAN On Wed, 21 Oct 2009, Zavodsky, Daniel (GE Capital) wrote: > Well, in my tests I have seen only a very slight improvement using the > NOOP IO scheduler on an enterprise storage array. Usually around 1-3%. Isn't the 'noop' scheduler recommended for use -inside- the virtual machines but not on the physical hosts -hosting- the virtual machines themselves? Vincent > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Domenico Viggiani > Sent: Tuesday, October 20, 2009 4:33 PM > To: 'Red Hat Enterprise Linux 5 (Tikanga) discussion mailing-list' > Subject: RE: [rhelv5-list] IO Scheduler and RAID HW or SAN > > * F M wrote: >> >> Fo years I left the default setting of our HDs IO scheduler. After >> reading some articles about HW RAID and SAN it seems to me that it is >> not a good thing to let Linux doing IO scheduling because the HW >> between him and the HDs have his own IO scheduler. >> >> I will probably run iozone to test with default and NOOP for example >> but I am curious if someone has some toughts on that subject ? > > I know that usage of NOOP scheduler is sometime recommended for > virtual machine hosting: > http://kbase.redhat.com/faq/docs/DOC-5428 > > > _______________________________________________ > rhelv5-list mailing list > [email protected] > https://www.redhat.com/mailman/listinfo/rhelv5-list > > _______________________________________________ > rhelv5-list mailing list > [email protected] > https://www.redhat.com/mailman/listinfo/rhelv5-list > -- ,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^` '~*-, Vincent S. Cojot, Computer Engineering. STEP project. _.,-*~'`^`'~*-,._.,-*~ Ecole Polytechnique de Montreal, Comite Micro-Informatique. _.,-*~'`^`'~*-,. Linux Xview/OpenLook resources page _.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~' http://step.polymtl.ca/~coyote _.,-*~'`^`'~*-,._ [email protected] They cannot scare me with their empty spaces Between stars - on stars where no human race is I have it in me so much nearer home To scare myself with my own desert places. - Robert Frost _______________________________________________ rhelv5-list mailing list [email protected] https://www.redhat.com/mailman/listinfo/rhelv5-list _______________________________________________ rhelv5-list mailing list [email protected] https://www.redhat.com/mailman/listinfo/rhelv5-list
