On Wed, October 21, 2009 12:53, Bob Friesenhahn wrote:
> On Wed, 21 Oct 2009, David Dyer-Bennet wrote:
>>> Device performance should be specified as a minimum assured level of
>>> performance and not as meaningless "peak" ("up to") values.  I repeat:
>>> peak values are meaningless.
>> Seems a little pessimistic to me.  Certainly minimum assured values are
>> the basic thing people need to know, but reasonably characterized peak
>> values can be valuable, if the conditions yielding them match possible
>> application usage patterns.
> Agreed. It is useful to know minimum, median, and peak values.  If
> there is a peak, it is useful to know how long that peak may be
> sustained. Intel's specifications have not characterized the actual
> performance of the device at all.

And just a random number labeled as "peak" really IS meaningless, yes.

> The performance characteristics of rotating media are well understood
> since they have been observed for tens of years.  From this we already
> know that the "peak" performance of a hard drive does not have much to
> do with its steady-state performance since the peak performance is
> often defined by the hard drive cache size and the interface type and
> clock rate.

It strikes me that disks have been developing rather too independently of,
and sometimes in conflict with, requirements for reliable interaction with
the filesystems in various OSes.  Things like power-dependent write
caches.  Boosts peak write but not sustained write, which is probably
benchmark-friendly, AND introduces the problem of writes committed to the
drive not being safe in a power failure.

David Dyer-Bennet, d...@dd-b.net; http://dd-b.net/
Snapshots: http://dd-b.net/dd-b/SnapshotAlbum/data/
Photos: http://dd-b.net/photography/gallery/
Dragaera: http://dragaera.info

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