[Simh] VAX Tape Emulation?

[Larry Baker]

Zane

> On Feb 20, 2018, at 9:00 AM, simh-request at trailing-edge.com wrote:
> 
> Date: Mon, 19 Feb 2018 21:55:00 -0800
> From: Zane Healy <healyzh at avanthar.com <mailto:healyzh at avanthar.com>>
> To: Zane Healy <healyzh at avanthar.com <mailto:healyzh at avanthar.com>>
> Cc: simh <simh at trailing-edge.com <mailto:simh at trailing-edge.com>>
> Subject: Re: [Simh] VAX Tape Emulation?
> Message-ID: <1665A095-D246-4272-91AC-EF2BBC45A1F7 at avanthar.com <mailto:1665A095-D246-4272-91AC-EF2BBC45A1F7 at avanthar.com>>
> Content-Type: text/plain; charset=utf-8
> 
> I’m backing MONK up over the Cluster to a “tape drive” on RENNY.


I'm really puzzled why you prefer to backup to a SIMH virtual tape image.  You can create empty SIMH VAX virtual disk drives for your clustered virtual VAX and backup directly to a save set on disk.  You can even make a backup disk image—bootable on a SIMH Alpha, when that arrives.  You can read files individually on a backup disk image any time you want to.  There is no need to go through the entire save set to find one file.

As far as your backup speed, you might be rate limited by the XOR blocks being added and by the (less likely) SIMH virtual tape formatting.  You should be able to test that by doing a backup on the SIMH VAX to the virtual tape drive to take the network out of the picture.  You can control how often XOR blocks are written, or eliminate them altogether.

Larry Baker
US Geological Survey
650-329-5608
baker at usgs.gov

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