Date: Wed, 19 Aug 2020 09:42:59 -0600 From: Gary Aitken <freebsd@dreamchaser.org> To: Manish Jain <bourne.identity@hotmail.com>, Polytropon <freebsd@edvax.de>, Christoph Kukulies <kuku@kukulies.org> Cc: Ruben via freebsd-questions <freebsd-questions@freebsd.org> Subject: Re: Correct way to disconnect/eject an USB hard disk ? Message-ID: <b9b46ecb-b1ef-8f67-7b41-ae3cf0d3864b@dreamchaser.org> In-Reply-To: <DB8PR06MB64427319E175193D1B828135F65D0@DB8PR06MB6442.eurprd06.prod.outlook.com> References: <C6B11926-65BE-4A05-B421-9F3E9C9AACF6@kukulies.org> <20200819142952.3686baa8.freebsd@edvax.de> <DB8PR06MB64427319E175193D1B828135F65D0@DB8PR06MB6442.eurprd06.prod.outlook.com>
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On 8/19/20 6:42 AM, Manish Jain wrote: > > > On 2020-08-19 17:59, Polytropon wrote: >>> After unmounting, are there any other measures to cleanly >>> disconnect the device? >> Usually not. If umount has been executed, and you wait a few >> seconds in order to let the command be finished successfully by the >> USB drive's firmware (last things to be written are _actually_ >> written), disconnect is possible at any time. The important thing >> to consider is that the filesystem should always be in a consistent >> state - that's what umount will accomplish. Due to the fact that >> "things need some time", waiting a few seconds is never wrong. >> After that, disconnecting power is no problem. > > > A note: it is perfectly safe to disconnect device any time after > umount has returned. The one problem is umount may take anything > between a second and a few hours (!) to return. This depends on > whether the filesystem was mounted as sync or async (the default). > > When fs is mounted with sync option on, I/O is very slow - ~10x > slower than with async. > > With async option on at the time of mount, I/O is much faster, the > algorithmic complexity of the code dealing with the I/O is much > higher, and a whole lot of data may remain unflushed even after an > I/O command (cp for instance) has returned. It is at the time of > umount all this data gets flushed - although you can manually force > the flush yourself with `sync`, in which case `umount` will return > quickly. Can you explain why I have seen umount commands return, and then the USB device "activity" light keeps blinking? I have on occasion waited for a while and it keeps blinking, and eventually I just unplugged it. Gary
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