Re: thin provisioned LUN support & file system allocation policy

[jim owens <jowens@hp.com>]

David Woodhouse wrote:
> On Fri, 7 Nov 2008, jim owens wrote:
> 
>> Ric Wheeler wrote:
>>
>>> The type of allocation that would help most is something that tries 
>>> to keep the lower block ranges "hot" for allocation, second best 
>>> policy would simply keep the allocated blocks in each block group hot 
>>> and re-allocate them.
>>
>> This block reuse policy ignores the issue of wear leveling...
>> as in most design things, trading one problem for another.
> 
> For SSDs we're being told not to worry our pretty little heads about 
> wear levelling. That gets done for us, with varying degrees of 
> competence, within the black box. All we can do to improve that is 
> pray... and maybe sacrifice the occasional goat.
> 

I'm talking DISK wear not SSD.  The array vendors who are causing
this problem are doing petabyte san devices, not SSDs.

Rewriting the same sectors causes more bad block remaps
until the drive eventually runs out of remap space.