On 7/8/05, Danny Cox wrote: > Erik, > > On Fri, 2005-07-08 at 14:00 +0200, Erik Slagter wrote: > > I am using softraid 1 on two sata disks and I'm trying to get the best > > possible performance. IMHO read actions (if properly addressed) should > > be split over the two drivers and performed independently. However, I > > don't notice anything to back this up. The read performance (with the > > dreaded hdparm) shows read performance on sda,sdb and md0 exactly the > > same. > ... > > What am I doing wrong here??? > > Nothing. I'll take a shot at answering this one instead of lurking > this time. Then, I'll crawl back under my rock. > > The raid1 driver keeps a "last visited block" for each drive. This is > the block number that was most recently read or written by that drive. > When a read request arrives, the driver examines each drive for the > nearest last visited block to the one requested. Guess what? If the > read starts with drive sda, then it will *always* be the one chosen to > service the read in the future, because the last visited block number is > only one off. This would only change if there are multiple processes > performing I/O on the md device. Then, it may switch to another drive. > In any case, it will *tend* to stick with the same drive. > > Did I explain that well, or only muddy the waters? > > -- > Daniel S. Cox > Internet Commerce Corporation >
Interesting. Unfortunately, I do a lot of sequential reading with little or no other computer activity and had wondered about the "slow" speed of RAID 1 on read. Does anyone know if that a common implementation on Hardware Raid controllers too? I have actually been working mostly with 3ware 7000 series cards, so the md implementation does not affect me, but if that is a common design then the 3ware card may have a similar algorithm. Greg -- Greg Freemyer The Norcross Group Forensics for the 21st Century - To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
