Re: thin provisioned LUN support

[Artem Bityutskiy <dedekind@yandex.ru>]

Ric Wheeler wrote:
> After talking to some vendors, one issue that came up is that the arrays 
> all have a different size that is used internally to track the SCSI 
> equivalent of TRIM commands (POKE/unmap).
> 
> What they would like is for us to coalesce these commands into aligned 
> multiples of these chunks. If not, the target device will most likely 
> ignore the bits at the beginning and end (and all small requests).
> 
> I have been thinking about whether or not we can (and should) do 
> anything more than our current best effort to send down large chunks 
> (note that the "chunk" size can range from reasonable sizes like 8KB or 
> so up to close to 1MB!).

Note, this is relevant to MMC as well. They have an "erase" command,
which is equivalent to discarding a group of sectors, e.g., 128KiB. So
we would speed MMC up if we could make sure our discard requests are:

1. 128KiB aligned
2. of 128KiB in size

P.S. Gropup size is MMC-specific.

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)
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