Re: patches for test / review

[Dan Nelson]

In the last episode (Mar 23), Greg Lehey said:
> 
> Agreed.  This is on the Vinum wishlist, but it comes at the expense of
> reliability (how long do you wait to cluster?  What happens if the
> system fails in between?).  In addition, for Vinum it needs to be done
> before entering the hardware driver.

For the simplest case, you can choose to optimize only when the user
sends a single huge write().  That way you don't have to worry about
caching dirty pages in vinum.  This is basically what the hardware
RAIDs I have do.  They'll only do the write optimization (they call it
"pipelining") if you actually send a single SCSI write request large
enough to span all the disks.  I don't know what would be required to
get our kernel to even be able to write blocks this big (what's the
upper limit on MAXPHYS)?

-- 
        Dan Nelson
        [EMAIL PROTECTED]


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