Date: Sat, 16 Feb 2019 10:08:32 -0700 From: Ian Lepore <ian@freebsd.org> To: Bruce Evans <brde@optusnet.com.au>, Gleb Smirnoff <glebius@freebsd.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r344188 - in head: lib/libc/sys sys/vm Message-ID: <259b30371291398891b48c38fc8231e7422f47e4.camel@freebsd.org> In-Reply-To: <20190217011341.S833@besplex.bde.org> References: <201902152336.x1FNaNUo039321@repo.freebsd.org> <20190217011341.S833@besplex.bde.org>
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On Sun, 2019-02-17 at 02:58 +1100, Bruce Evans wrote: > Slowness is relative. In FreeBSD-1, floppy disk devices were still in > use and were especially slow. Now hard disks are slow relative to fast > SSDs. But the number of buffers was unchanged. It is still essentially > unchanged except for vn pager pbufs. The hard disks can complete 128 > i/o's for a full queue much faster than a floppy disk, so the relative > slowness might be similar, but now there are more subsystems and some > systems have many more disks. The modern replacement for a floppy disk in this regard is an sdcard. When doing large numbers of random writes, such as untarring a snapshot of rootfs to a ufs filesystem on sdcard, gstat will show ms/w values anywhere from 30,000 to 90,000 depending on the card. It stays that way throughout the operation, and IO to all other disks on the system essentially comes to a standstill. This is true whether the card is in a native sdhci controller or a usb-attached multiformat reader/burner. -- Ian
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