We've installed an LSI Logic MegaRaid SCSI 320-1 card on our server (used only temporarily to move data to larger disks, but that's not the point), and measured linear write performance, just to know how much time it will took to copy our (somewhat large) data to the new array. And to my surprize, this card, with current firmware, current (2.6.15) kernel and modern disks is terrible slow on writing - writing speed varies between 1.5 megabutes/sec to 10 megabytes/sec, depending on the logical drive settings in the megaraid adapter. I tried different raid configurations (raid10 - 3 spans of two-disk raid1s; raid1 out of 2 drives; raid 0 on one drive) - makes no difference whatsoever (but on raid1, I only can get 8 megabytes/sec write speed - 10 mb/sec is on raid10). The disks are 140Gb FUJITSU MAT3147NC ones, pretty modern. One disk, when plugged into non-megaraid card and accessed as single disk, delivers about 60 megabytes/sec write speed, and about 80 mb/sec read (reading speed on megaraid array is quite good - about 240 mb/sec for 6-disk raid10). I've upgraded firmware on the megaraid card to the latest one available on lsi logic website - nothing changed wrt write speed (but read speed decreased from 240 to about 190 mb/sec - still acceptable for me). I'm using megaraid_mbox driver. The only "improvement" I was able to get is when I enable write caching on the card, -- in this case, writing speed is very good up to first 64Mb (amount of memory on the card), and decreases again back to 1.5..10 mb/sec after 64Mb. The question is: where's the problem? linux? driver? hardware? Anyone else expirienced this problem? Thanks. /mjt - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
