jwf@munsell.UUCP (Jim Franklin) (12/19/86)
I agree with Don Speck -- the problem with raw disk thruput is lost disk rotations. The reason for lost rotations is obvious, considering the limits placed on transfer size by minphys(), and the sheer amount of code that has to be executed for each block transfer: physio(): while ( useless iovec trash ) { while ( more bytes in buffer ) { calculate transfer count via (*mincnt)(); (which is lock in buffer; usually physstrat(); minphys) allocate kernelmap; mapin(buffer); (*disk_strategy)(); disk_sort(); issue disk command; sleep() until B_DONE; mapout(buffer); free kernelmap; unlock buffer; } } We are running SUN-3's with Fujitsu M2361A's and Interphase VSMD 4200 "Cheetah" VME controller boards. For raw i/o, our maximum transfer rate is 1.2 megabytes/sec writing, 1.5 megabytes/sec reading. Note that the theoretical maximum transfer rate for this drive (M2361A) the way we formatted it is ( 60 revs/second * 64 sectors/track * 512 bytes/sector ) or 1966080 bytes/sec. This gives a raw write transfer of 63% maximum, and a raw read transfer of 77% maximum. I consider this mediocre performance, considering the capabilities of the drive and the controller. ----- {harvard!adelie,{decvax,allegra,talcott}!encore}!munsell!jwf Jim Franklin, Eikonix Corp., 23 Crosby Drive, Bedford, MA 01730 Phone: (617) 275-5070 x415