I'd say you're about right on the mark after you figure in compression.
For example, the minimum speed of an LTO-3 drive is 27 MB/s, and its
native speed is 80 MB/s.  A T10000 has a native speed of 120 MB/s, but
can step down to a native speed of 40 MB/s.  

But then you have to add compression. After you add what I'd consider to
be an average compression ratio (1.5:1), your 30-35% becomes about 50%
of the drive's original advertised native speed.

Does that make sense?

---
W. Curtis Preston


-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of
Richard Sims
Sent: Wednesday, May 23, 2007 12:38 PM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Re: [ADSM-L] Restore Times

On May 23, 2007, at 3:21 PM, Paul Zarnowski wrote:

> ... LTO2+ has variable speed technology,
> which helps, but I think only to a limit.  I think there may still be
> a point where if the data is being read too slowly, the drive will
> stop streaming.

 From what I've read, drives can reliably reduce speed only to about
50%, so speed-matching is a very limited thing.  Collocation and
concerted reclamation of serial media need to be in effect to keep
restorals as efficient as possible.  Reclamation is usually thought
of as a means of supplying the scratch pool, but its value as a
restoral performance aid needs to also be kept in mind.

    Richard Sims