'mkfs(1m)' for RA81s - gap?

[lou at AEROSPACE.ARPA]

From:  Lou Nelson <lou at AEROSPACE.ARPA>

>Return-Path: <ihnp4!houxm!garys at UCB-VAX.ARPA>
>Date: 6 Oct 84 5:13:30-PDT (Sat)
>To: Unix-Wizards at BRL-VGR.ARPA
>From: ihnp4!houxm!garys at UCB-VAX.ARPA
>Subject: 'mkfs(1m)' for RA81s - gap?
>
>Article-I.D.: houxm.926
>
>Several sources have come up with varying opinions about the optimal
>Gap Size and Blocks/cylinder for DECs RA81 drives. We're under the
>assumption of 728 Blocks per cylinder (14 R/W heads x 52 sectors/track).
>
>If 728 is correct, what should the proper gap size be considering
>3600 RPM?
>
>Thanks in advance.
>
>Gary Seubert - HOCC
>[..ihnp4!]houxm!garys
>
>(running System V if it makes a difference)

I'm not really a wizard, but here goes anyway.  It does make a 
difference that you are running System V, since unlike 4BSD I
think only 1 block is read in at a time.  So your 728 is probably
correct.  The "gap size" is the important number however and, using
a program posted by mh3bs!agp on 11/19/83 (who in turn got it from
a USENIX paper), I measured 9 as the value that gave the best
performance on my RA81s before I kicked them out the door in favor
of Eagles.  If you wish, assuming this reaches you, I can send you
my modification of that program that includes RA81s and Eagles and
you can run some experiments to determine which numbers are best
for your configuration.  
Regards,
Lou