RAID and UPS

There's my good ol' American Power Conversion UPS (uninterruptible power supply) sitting in the corner. Not far away is a Seagate Black Armor NAS. There's a cable that goes from the data port on the UPS to a USB port on the RAID box. This is used to gracefully power down the RAID in the event of a power outage after the electricity has been out for xx (fill in your number) minutes. So far, so good.

Suppose now that I buy a second RAID (which I'll use to mirror the first). Can I split that data signal from the UPS (most likely through a hub) so it talks to both RAID boxes? Or should I simply buy another UPS for the second RAID system?

If the UPS is the USB host, you might be able to split it like that, otherwise I don't think so. There might be some adapters to connect multiple RAIDs, though, you should probably ask UPS.

DotCom Editor said:

Suppose now that I buy a second RAID (which I'll use to mirror the first).

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why would you want to mirror a RAID array?

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Asposium said:

why would you want to mirror a RAID array?

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Because one RAID array still represents a single point of failure. If a drive in the array fails, you have to replace the drive and rebuild the array. No problem. But that can take many hous, during which the data may not be available. Having a mirrored array ensures uninterrupted access to data. BUT, here's the really bad part that people overlook: During the process of rebuilding the array, the remaining drives are working continuously, with far more head movement than under normal circumstances. Should one of those drives fail during the rebuild process, you have now lost ALL your data. So, you must have your data backed up somewhere else.

Most modern NAS RAID devices have twin Ethernet ports. One is for connecting to the network. The other is for connecting the two arrays directly to each other, bypassing the network. This is done to provide a mechanism for the two arrays to stay in sync without placing any burden on the network bandwidth. As a result, whatever you save to array #1 is automatically saved to array #2.

Bottom line: Never, ever, ever store your data in only location.

Buying a second UPS is the simplest solution. Your other solution is not viable. It is theoretically possible to get one NAS to tell the other one to shut down over ethernet - nut (under linux) can do this - but whether it is practical in your situation depends on your nas.

DotCom Editor said:

BUT, here's the really bad part that people overlook: During the process of rebuilding the array, the remaining drives are working continuously, with far more head movement than under normal circumstances. Should one of those drives fail during the rebuild process, you have now lost ALL your data. So, you must have your data backed up somewhere else.

Click to expand...

Absolutely, always keep two backups on different locations. A fire or flood will destroy 50 copies if they are all in the same location.

Also, if you're that worried about a drive failure during rebuild, why not use RAID 6 ? Around here that's what we do for any array over 8 drives.