On 07/19/2013 11:21 AM, John R Pierce wrote:
> On 7/19/2013 11:07 AM, Gordon Messmer wrote:
>>> >>- under provision (only use 60-75% of drive, leave unallocated space)
>> >That only applies to some drives, probably not current generation hardware.
>> >
> it applies to all SSDs. they NEED to do write block remapping, if they
> don't have free space, its much much less efficient..
Well, maybe.
The important factor is how much the manufacturer has over-provisioned
the storage. Performance targeted drives are going to have a large
chunk of storage hidden from the OS in order to support block remapping
functions. Drives that are sold at a lower cost are often going to
provide less reserved storage for that purpose.
So, my point is that if you're buying good drives, you probably don't
need to leave unpartitioned space because there's already a big chunk of
space that's not even visible to the OS.
Here are a couple of articles on the topic:
http://www.edn.com/design/systems-design/4404566/Understanding-SSD-over-provisioning
http://www.anandtech.com/show/6489/playing-with-op
Anand's tests indicate that there's not really a difference between
cells reserved by the manufacturer and cells in unpartitioned space on
the drive. If your manufacturer left less space reserved, you can
probably boost performance by reserving space yourself by leaving it
unpartitioned.
There are diminishing returns, so if the manufacturer did reserve
sufficient space, you won't get much performance benefit from leaving
additional space unallocated.
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