Date: Sun, 30 Aug 2015 18:22:37 +0200 From: Polytropon <freebsd@edvax.de> To: Warren Block <wblock@wonkity.com> Cc: freebsd-questions@freebsd.org Subject: Re: Replacing Drive with SSD Message-ID: <20150830182237.5a39e04c.freebsd@edvax.de> In-Reply-To: <alpine.BSF.2.20.1508300633160.44682@wonkity.com> References: <CEAD84AD-341A-4FB9-A3A1-D0D5A550AFFD@lafn.org> <alpine.BSF.2.20.1508281235390.74312@wonkity.com> <20150829220311.c7608be1.freebsd@edvax.de> <alpine.BSF.2.20.1508300633160.44682@wonkity.com>
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On Sun, 30 Aug 2015 06:58:42 -0600 (MDT), Warren Block wrote: > On Sat, 29 Aug 2015, Polytropon wrote: > > > On Fri, 28 Aug 2015 12:47:30 -0600 (MDT), Warren Block wrote: > >> If you are a belt-and-suspenders type, create a smallish, maybe 4G, > >> partition on the drive that will never be used and leave it empty. > >> Don't write to it, ever. This is called over-provisioning. The drive > >> sees that all those blocks are free and it can swap them around for wear > >> leveling. This can be used in addition to trim. > > > > To extend the idea (because sometimes I am the axe-and-byrnie type): > > Does this also work with _no_ partitions at all? For example, when > > the device is formatted "as a whole" (dedicated), like > > > > # bsdlabel -w ada0 > > # bsdlabel -e ada0 > > set type "4.2BSD" for 'a' partition > > make 'a' same size as 'c' > > save > > # newfs -m 0 -i 16384 -b 16384 -f 2048 -U -t enable -n disable -L ssdroot /dev/ada0a > > # bsdlabel -B ada0 > > > > where /dev/ada0a has been prepared with bsdlabel to span the entire > > device (as in the example) - or in this case, to be a little bit > > less (4G) than the whole disk capacity? > > Making a partition for free space is one way. Another way is to leave > part of the drive unpartitioned. Either one just guarantees there is a > good supply of unused blocks available to the drive. Thanks for this answer. I will probably use this approach when new SSDs come into use here (for single-user all-in-one laptop systems typically). > I'm fairly sure that UFS does not write to every block under its control > even during a format. Correct, it doesn't. It simply initializes a subset of locations on disk and leaves the majority of allocated disk space untouched. It will receive writes as soon as there are _actual_ writes to the file system. That's one of the reasons newfs is so damn fast even if you format a 2 TB hard disk. :-) > Until written as part of a file, those blocks are > also known to be unused. So forcing extra unused space is probably > unnecessary most of the time. Still I believe it's a good idea to have some "spare space" available that is guaranteed to _not_ go into use. -- Polytropon Magdeburg, Germany Happy FreeBSD user since 4.0 Andra moi ennepe, Mousa, ...
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