I use DSUs for network media servers and either DSUs or VTL for large clients that need to be dedicated media servers. Here are some things to consider with network based backups: Using VTL: A slow network client will hold onto a VTL tape. The other images on that tape are then not available for duplication which means if there was a data center disaster those images would not have been copied to tape yet. This impacts your RPO. Using DSU: A slow client will only effect the duplication of its image and not the image of other clients. I use VTL on large clients to save money. Under a DSU methodology I must allocate the san storage directly to the host in a multiple of the size of prod disk space. As the prod space grows the DSU space needs to grow. This must be monitored, managed, and sustained. There are hundreds of these types of clients across many data centers. In addition, that allocated DSU space is not available for any other media server so there is a lot of unused, yet allocated storage, and with no compression. With VTL I can put that head in front of the same storage and zone the virtual drives to the media servers. The VTL arbitrates the access and provides a shared storage resource accessible over a high speed SAN. I have the ability to increase backup storage capacity without touching a production client. In addition I get compression on that storage.
__________________________________________ Jonathan Marianu (mah ree ah' nu) AT&T Storage Planning and Design Architect (360) 597-6896 Work Hours 0800-1800 PST M-F Manager: Jim Taylor (dt3249) (678) 893-3170
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