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Cool Blog: A Different Approach to HSM

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By Richard Jones

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Posted: 13 Jul 2006
 

Cool Blog: A Different Approach to HSM
by Richard Jones

In my last post, I talked about what I don?t like about HSM. Well, I talked this over with our engineers and as good engineers go, they came up with an idea. They called it Shadow Volumes, and its planned to be a new feature in the next release of OES (code named Cypress). What's cool about it is that it gives you what you want with HSM without the problems that come with traditional HSM. It gives you the ability to put older data on less expensive SATA drives and archive it infrequently, and restore it later (in case of a disaster). While putting the active data on more expensive drives and backing it up daily, or even replicating it for better protection. So this sounds like HSM, but it doesn't leave file stubs. How does it work? It effectively combines the contents of two or more separate storage locations (which have identical subdirectory structures). The primary storage contains the active files that need to be protected. The secondary or tertiary storage contains older inactive files, or files of types you don't want to protect (those pesky MP3s). All storage volumes have the same subdirectory structure, and that structure is maintained consistent by Shadow Volumes. A virtual directory is created for the users or application which combines the contents of the primary, secondary and other actual storage. Since it has no file stubs, there's no need to demigrate data if a index search is performed (the Google desktop problem), as the stale files can be read at any time from their respective storage, and don't need to be moved to primary ever.

What's also nice, is that the primary, secondary, etc. storage that is behind shadow volumes are all standard volumes, meaning you can use anyone's backup/restore or replication software to protect it, as well as any other tools. This is unlike traditional HSM which usually forces you to use the HSM vendor's tools to replicate, archive or otherwise further protect the migrated file data.

So with Shadow volumes, in the simplest case, you have three views of data: Two physical (primary and secondary volumes) and a virtual combined view. The users/applications are pointed to the virtual combined view. You then point your backup/protection software at the physical views. This allows you to apply differing levels of protection based on the characteristics of the data. You can also apply different restore priorities in case of a disaster recovery. Restore the primary data immediately, and then restore the secondary when you can get to it (even weeks later). How do you create a shadow? For those of you who have used the Storage Resource Management utilities built into NetWare Remote Manager (OES NetWare, and OES Linux since SP2), that's what you use to inventory and specify the criteria for what will be moved and when.

So when OES 2 comes out in Beta, take a look at the Shadow Volume feature. You can set it up on the same server, or have it point through a simple mount point to a different server.

This feature is only available on OES Linux, and initially only for the NCP server. But it looks really cool and we are working to expand protocol and application support.

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