[dm-devel] sparse target

[Heinz J . Mauelshagen]

EVMS team (Steve or Corry are the ones to ask i guess),

Joe mentioned that you are implementing a sparse and a bbr target
for device-mapper.
I've got a couple of questions for you.

1. Is it read-only or read-write sparse?

1b. If it's read-write sparse it must allocate storage dynamically on
    writes kicking of a user space allocator waiting for those writes
    on a table event queue, right?


2. I assume that the bbr target uses preallocated and inaccessable table space
   (inaccessable in terms of regular io queued to the bbr target) to be
   allocated on the fly on io error?

2a. If that allocation happens, do you send an event to update metadata in user
    space in order to reflect the relocation?

2b. How do you guarantee that that update is atomic?

2b. Preallocation is fine to gain performance. Additionally you guys must be
    planning to stack bbr onto sparse (presuming read-write sparse), right?


Regards,
Heinz    -- The LVM Guy --

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Heinz Mauelshagen                                 Sistina Software Inc.
Senior Consultant/Developer                       Am Sonnenhang 11
                                                  56242 Marienrachdorf
                                                  Germany
Mauelshagen at Sistina.com                           +49 2626 141200
                                                       FAX 924446
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