Replacing Drive with SSD

Warren Block wblock at
Sun Aug 30 12:58:55 UTC 2015

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.

I'm fairly sure that UFS does not write to every block under its control 
even during a format.  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.

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