Re: hole punching performance

["Bradley C. Kuszmaul" <kuszmaul@xxxxxxxxx>]

So my understanding is that the first time I do a read() I'll have to read the extents.  My writes are on the order of a megabyte, a 250MB file will likely require an extra I/O to open.  That's fine.

It really has been helpful to have all this performance-modeling information.  

Thanks.

-Bradley

On Tue, Jan 15, 2013 at 5:54 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote:

On Tue, Jan 15, 2013 at 04:34:50PM -0500, Bradley C. Kuszmaul wrote:
> So does it cost a lot to read all the extents just to read the first block?

Depends on the number of extents in the file. Figure an IO per 250
extents for a 4k block size filesystem (extent records are 16 bytes
in size on disk).

Cheers,

Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx

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