Date: Mon, 25 Oct 2004 13:49:10 -0600 From: Scott Long <scottl@freebsd.org> To: Charles Swiger <cswiger@mac.com> Cc: freebsd-current@freebsd.org Subject: Re: FreeBSD 5.3b7and poor ata performance Message-ID: <417D58B6.5030509@freebsd.org> In-Reply-To: <77F3FD4D-26BE-11D9-9A2F-003065ABFD92@mac.com> References: <14479.1098695558@critter.freebsd.dk> <417D25E8.6080804@ng.fadesa.es> <200410251928.01536.victor@alf.dyndns.ws> <200410251837.58257.Thomas.Sparrevohn@btinternet.com> <417D3F12.20302@DeepCore.dk> <417D40A1.9030802@ng.fadesa.es> <417D45F1.9090504@freebsd.org> <77F3FD4D-26BE-11D9-9A2F-003065ABFD92@mac.com>
next in thread | previous in thread | raw e-mail | index | archive | help
Charles Swiger wrote: > On Oct 25, 2004, at 2:29 PM, Scott Long wrote: > >>> Also, there is an unresolvable question. Why two 52MB/s disks >>> in raid0 has a throughput of 40MB/s and for raid1 18MB/s?? >> >> >> Would you _PLEASE_ stop trying to associate RAID with performance! >> RAID is about reliability and reduncdancy, not about speed. > > > All RAID modes make tradeoffs between performance, reliability, and cost. > > RAID-1 mirroring and RAID-5 provide higher reliability by using partial > or full redundancy. However, RAID-0 striping provides no additional > reliability: the primary reason for using RAID-0 is to improve > performance by accessing two or more devices in parallel. > >> Some cases can give you desirable performance increases as a side effect, >> but that is not the primary goal. > > > Disagree. Why else would you use RAID-0 striping? > > [ If you simply want to create a logical volume bigger than the size of > a physical drive, you can use concatenation instead. ] > >> Specifically in this case, the >> GEOM raid classes are fairly new and have not had the benefit of >> years of testing. I'd much rather that the focus be on stability >> and reliability for them, not speed. Once the primary goals of >> RAID are satisfied then we can start looking at performance. > > > Your position is certainly reasonable: if a storage system is not > reliable, how fast it performs is something of a moot point. :-) > However, this being said, a RAID-0 implementation needs to improve > performance compared with using a bare drive if it is to be useful. > Well, RAID-0 is a special case =-) That said, putting discrete RAID classes into the GEOM layer is something of a new adventure, so I'm not surprised to hear about performance problems, even in RAID-0. There might be extra data copies or path latencies that weren't planned for or expected. It's definitely something to look at. But it's also a very new subsystem, so it would be unfair to judge FreeBSD performance with it. Scott
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?417D58B6.5030509>