Really appreciate all of the valuable input. The current server has the Perc4ei controller. The impression I am taking from the responses is that we may be okay with software raid, especially if raid 1 and 10 are what we intend to use. I think we can collect enough information from the archives of this list to help make decisions for the new machine(s), was just very interested in hearing feedback on software vs. hardware raid. We will likely be using the 2.6.18 kernel. Thanks for everyone's input, Joe -----Original Message----- From: Scott Marlowe [mailto:smarlowe@xxxxxxxxxxxxxxxxx] Sent: Tuesday, February 27, 2007 12:56 PM To: Joe Uhl Cc: pgsql-performance@xxxxxxxxxxxxxx Subject: Re: [PERFORM] Opinions on Raid On Tue, 2007-02-27 at 07:12, Joe Uhl wrote: > We have been running Postgres on a 2U server with 2 disks configured in > raid 1 for the os and logs and 4 disks configured in raid 10 for the > data. I have since been told raid 5 would have been a better option > given our usage of Dell equipment and the way they handle raid 10. Some controllers do no layer RAID effectively. Generally speaking, the cheaper the controller, the worse it's gonna perform. Also, some controllers are optimized more for RAID 5 than RAID 1 or 0. Which controller does your Dell have, btw? > I > have just a few general questions about raid with respect to Postgres: > > [1] What is the performance penalty of software raid over hardware raid? > Is it truly significant? We will be working with 100s of GB to 1-2 TB > of data eventually. For a mostly read system, the performance is generally pretty good. Older linux kernels ran layered RAID pretty slowly. I.e. RAID 1+0 was no faster than RAID 1. The best performance software RAID I found in older linux kernels (2.2, 2.4) was plain old RAID-1. RAID-5 was good at reading, but slow at writing.
