(9915) Shadow Copies and HBMM, Volumes, File Structures

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(9915) Shadow Copies and HBMM, Volumes, File Structures

Post by User » Mon Nov 08, 2004 8:26 am

We've used volume shadowing for OpenVMS V7.3-2 for cross-site mirroring of 18GB disk. It usually takes 3-4 hours to shadow copy the 18GB disk set and smaller disk such as 9GB or even 18GB is not available in the market. Actually, only half of the 18GB disk has been used but the volume shadowing simply just shadow copy the entire 18GB. Could we simply use the command below provided in V7.3-2 to initialize the total block size of shadowed 18GB disk to 9GB such that it would only
shadow copy 9GB data instead of 18GB?

On node A

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$init/size=18000000 $1$dkb100 18GDSK
On node B

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$init/size=18000000 $2$dkb100 18GDSK
$mount dsa1/shadow=($1$dkb100,$2$dkb100)18GDSK
Last edited by marty.stu on Wed Aug 10, 2022 9:16 am, edited 1 time in total.


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Re: (9915) Shadow Copies and HBMM, Volumes, File Structures

Post by Wizard » Tue Nov 09, 2004 8:26 am

Host-based minimerge (HBMM) would be the approach considered by the OpenVMS Wizard. HBMM support is available via ECO kit for V7.3-2. A secondary approach would involve a controller capable of providing partitioned-device support (and hardware-level RAID) operating with volume shadowing. Or yes, INITIALIZE/SIZE.

Volume shadowing operates at the volume level and largely outside the file structure; that written, INITIALIZE/SIZE and the associated Dynamic Volume Expansion (DVE) support very confusingly also establishes the effective device size for shadowing and other volume-level operations, and will provide the desired effect of reducing the aggregate amount of disk data requiring shadowing. While shadowing operates at the volume level, the INITIALIZE/SIZE command operates outside the normal command expectations and configures both the file structure layered on the disk volume, and the effective volume size. (It might be more obvious to consider the SET VOLUME/LIMIT and /SIZE mechanism, than the INITIALIZE/SIZE command.)

Smaller SCSI devices are also readily available on the used-equipment market, and storage controllers are available that will present the appearance of smaller disks; that support hardware-level disk partitioning. These would operate with volume shadowing of course, and would reduce the volume of data transferred for a shadow copy.
Last edited by marty.stu on Wed Aug 10, 2022 9:17 am, edited 1 time in total.

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