I'm looking to replace our current storage. The existing system is just a 450GB file share on our 7yr old domain controller, plus another 150GB from another server. We map these to drives on the client machines. Both back up to a single 400GB tape drive. Add in a few system states and a sql server db and the nightly backup is up around 600GB. This is more than a single tape will do, and so we currently have a staggered backup where we only take a "full" from 1/5 of the total space each weeknight + a differential of everything.
To replace this, I want to go to two dedicated servers (primary, plus mirror and backup in one). The plan for the first is a RAID 1 volume for the OS + 2 RAID 10 2TB volumes for data (4 disks + 1 hot spare each, 12 1TB disks total including OS). The plan for the other is to have the same 12 1TB disks (mirrored from the first server each night). It will also have 2 6TB RAID 6 volumes (5 2TB disks each, separate volumes to improve the inevitable rebuild times) that I plan to use our existing backup exec software to make a differential snapshot each night. This will provide historical/generational storage for a true backup in place of our tape, and should be enough space to get about 30 days worth (a simplistic check of our change rate shows I need about a 3:1 ratio to accomplish this). The 2nd server will live on the far side of campus to avoid the need to take anything off site.
I'd much rather buy a vendor-supported solution, but cost is a huge issue here. I know I can do what I've described above for a total cost of around $13,000 (including OS licensing, thank you academic pricing for educational institutions), which places it way below any commercial option I've seen. I have a reliable partner for the basic chassis, RAID cards, and backplane, so I know I'm getting good equipment there, and I know I need a quality RAID card. I just haven't built a server of this scale before, and hence my questions:
Is there anything I'm missing that leaves me unnecessarily open to data loss? Anything I should look to do or avoid when assembling, installing, and configuring the servers? Nothing has been purchased yet, so I'm open to alternate suggestions — but the pricing is key. Some items that catch my eye right off the bat that I'd appreciate comment on:
- To reduce backup time/stress on the primary, I'd like to take the nightly backup from the mirror. But will copying to the mirror destroy the archive bit I need to get good differentials/incrementals?
- I'm not sure exactly how to configure the generational storage here, since both differential and incremental need a base to work from. I know I can use the primary storage directly for this, and that's not a big deal for a file here and there, but what if I need to do a complete rebuild of a volume? How do I make sure that files that don't change for 30 days are still available?
- The solution I just described requires 44TB of raw disks space, but only exposes 4TB to my users. The rest is lost to RAID, mirror, and historical backup space. Can I safely do better than that 11:1 ratio?