Re: [TUHS] /dev/drum

On 23 Apr 2018 17:30 -0600, from tuhs(a)minnie.tuhs.org (Grant Taylor via TUHS): I couldn't quite resist, so tried it out. Take this for what it is, an anecdote. Reading 10 GB in direct mode using dd with no skip at the beginning, in 1 MiB blocks, gives me about 190 MB/s on one of the Seagate SAS disks in my PC, and some 165 MB/s on one of the HGST SATA disks in the same PC. Obviously, that's for purely sequential I/O, with very little other I/O load. Doing the same with an initial skip of 3,500,000 blocks (these are 4 TB drives, so this puts the read toward the outer limit), I get 105 MB/s on the Seagate SAS and 100 MB/s on the HGST SATA. I did the same thing twice to make sure caching wasn't somehow interfering with the values. The differences for all reported transfer rates were marginal, and well within a reasonable margin of error. That's definitely statistically significantly slower toward the outer edge of the disk as presented by the OS. That _should_ translate to slower for higher LBAs, but with all the magic happening in modern systems, you might never know... Of course, back in ye olden days, even 100 MB/s would have been blazingly fast. Are we spoiled these days to think of throughputs on the order of a gigabit per second as slow? -- Michael Kjörling • https://michael.kjorling.se • michael(a)kjorling.se “The most dangerous thought that you can have as a creative person is to think you know what you’re doing.” (Bret Victor)