From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: raid10 vs raid5 - strange performance Date: Sat, 29 Mar 2008 16:25:31 -0400 Message-ID: <47EEA5BB.5080106@tmr.com> References: <20080325233649.GA632@rap.rap.dk> <20080326072416.GA8674@rap.rap.dk> <20080326192935.GB18621@rap.rap.dk> <47EAACAB.7070203@tmr.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Christian Pernegger Cc: Linux RAID List-Id: linux-raid.ids Christian Pernegger wrote: >> After doing a little research, I see that the original slowest form of PCI >> was 32 bit 33MHz, with a bandwidth of ~127MB/s. >> > > That's still the prevalent form, for anything else you need an (older) > server or workstation board. 133MB/s in theory, 80-100MB/s in > practice. > > I just looked at a few old machine running here, ASUS P4P800 (P4-2.8 w/HT), P5GD1 (E6600), and A7V8X-X (Duron) boards, all 2-5 years old, and lspci shows 66MHz devices on the bus of all of then, and the two Intel ones have 64-bit devices attached. >> The most common hardware used the v2.1 spec, which was 64 bit at 66MHz. >> > > I don't think the spec version has anything to do with speed ratings, really. > > That was the version which included 66MHz and 64-bit. I believe any board using 184, 200, or 240 (from memory) RAM is v2.1, and probably runs a fast bus. Pretty much anything not using PC-100 memory. See wikipedia or similar about the versions. >> I would expect operation at UDMA/66 >> > > What's UDMA66 got to do with anything? > > Sorry, you said this was a PATA system, I was speculating that your drives were UDMA/66 or faster. Otherwise the disk may be the issue, not the bus. Note: may... be. >> Final thought, these drives are paired on the master slave of the same >> cable, are they? That will cause them to really perform badly. >> > > The cables are master-only, I'm pretty sure the controller doesn't > even do slaves. > > Good, drop one possible issue. > To wrap it up > - on a regular 32bit/33Mhz PCI bus md-RAID10 is hurt really badly by > having to transfer data twice in every case. > - the old 3ware 7506-8 doesn't accelerate RAID-10 in any way, even > though it's a hardware RAID controller, possibly because it's more of > an afterthought. > > > On the 1+0 vs RAID10 debate ... 1+0 = 10 is usually used to mean a > stripe of mirrors, while 0+1 = 01 is a less optimal mirror of stripes. > The md implementation doesn't really do a stacked raid but with n2 > layout the data distribution should be identical to 1+0 / 10. > The md raid10,f2 generally has modest write performance, if U is a single drive speed, write might range between 1.5U to (N-1)/2*U depending on tuning. Read speed is almost always (N-1)*U, which is great for many applications. Playing with chunk size, chunk buffers, etc, can make a large difference in write performance. -- Bill Davidsen "Woe unto the statesman who makes war without a reason that will still be valid when the war is over..." Otto von Bismark