From mboxrd@z Thu Jan 1 00:00:00 1970 From: michael@kjorling.se (Michael =?utf-8?B?S2rDtnJsaW5n?=) Date: Tue, 24 Apr 2018 09:37:09 +0000 Subject: [TUHS] /dev/drum In-Reply-To: <866bbea1-3a26-20a4-e233-1b8dc0ea2683@spamtrap.tnetconsulting.net> References: <7wfu3nuqeb.fsf@junk.nocrew.org> <3A18DFEC-42B7-4234-9DD1-367733270D50@tfeb.org> <0abe01d3db28$b6573660$2305a320$@ronnatalie.com> <866bbea1-3a26-20a4-e233-1b8dc0ea2683@spamtrap.tnetconsulting.net> Message-ID: <20180424093709.GB7568@h-174-65.A328.priv.bahnhof.se> On 23 Apr 2018 17:30 -0600, from tuhs at minnie.tuhs.org (Grant Taylor via TUHS): > On 04/23/2018 04:15 PM, Warner Losh wrote: >> It's weird. These days lower LBAs perform better on spinning >> drives. We're seeing about 1.5x better performance on the first >> 30% of a drive than on the last 30%, at least for read speeds for >> video streaming.... > > I think manufacturers have switched things around on us. I'm used > to higher LBA numbers being on the outside of the disk. But I've > seen anecdotal indicators that the opposite is now true. 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 at 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)