On Sat, Sep 08, 2012 at 12:35:22PM -0400, Mikulas Patocka wrote:
> Your changes are ok, it could be included in the kernel.
>
> Regarding flushes ... could you please explain how write-back caching
> works in your design?
We are not actually using write-back caching in our design at all, but
assumed that for a general-purpose DM device like dm-switch, some
underlying storage may rely on REQ_FLUSH to ensure proper data
synchronization, so the switch should do the right thing when required.
The code is modeled on dm-stripe.
> Is there some write-back cache in the host adapter?
No, there is not at this time.
> Is there some write-back cache in the individual storage nodes? (i.e. does
> the node signal end of I/O before it finishes writing data to the disk)
No, there is not at this time. The iSCSI-backed SD devices we are
ultimately using do not advertise any write-back cache ('sdparm
--get=WCE' returns 0).
> Another thing - please resend your code with "Signed-off-by". Read the
> meaning of "Signed-off-by" in Documentation/SubmittingPatches, agree to
> the terms and append "Signed-off-by: Jim Ramsay <jim_ramsay@xxxxxxxx>" to
> the code. It is a legal requirement, so that you certify that the code is
> under the open source license and that you have the right to distribute
> the code.
Will do shortly. Thanks!
--
Jim Ramsay
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