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Currently, I have 4 hard disks which have been configured as RAID 1+0 in HP Proliant 380 G7, SmartArray p410i. I am planning to buy other new 8 hard disks to replace old array by swapping the disks out and keep the old array as backup. I also make full backup and I will use this backup to restore to new 8 hard disk array. Can I still use the old 4 disks if I already configured RAID 1+0 with new 8 disks?

So if I decide I want to go back to the old array (for example restore to the new array failed), I can just take the new array 8 disks out, put the old array 4 disks in and the data will be readable?

I did the research on HP Business Communities forum and they said it is possible to do that without data lost. they instructed to start the server without any disk and try clear any configuration exists then put previous disks back which was installed on the server in the correct slots if possible.

May someone confirm this that it really works?

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Most modern Most Hardware RAID controllers seem to write the array configuration the the disks (rather than keep it in some NVRAM on the card). Which means that in practise this will work if you put the discs back on the same or same series RAID card. (Which is nice to known, but alas not a direct confirmation. I never tried this with a P410i) - And unless you have some sort of encryption on the drives, keep the old drives in a safe or similar places as you keep your backups. –  Hennes Aug 8 '12 at 4:56
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You can't test it to make sure it works first? You really should. Take a backup, pull the drives, create your new array, pull those drives, and then pop the original array back in. If it works, great, if not, you can restore from backup. –  HopelessN00b Aug 8 '12 at 5:05
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1 Answer

HP Smart Array solutions keep the RAID configuration on disk. If you remove the old disk set and keep the drives in order (labeled 1 through 4), you can use them with any similar-generation controller. They would still constitute a bootable array/logical drive.

When you talk about keeping the old disks as a backup, are you just thinking about using it as a fall-back solution? But you still have a backup process in place... What would happen to the 4 disks after you migrate?

Why are you moving to 8 disks? Space? Speed?

You could safely replace the 4 disks with 4 of the larger disks (assuming that they're larger) and add the additional 4 disks. From there, you could perform an online RAID resize/transformation that will redistribute data across the new drives.

This can be done entirely online without any downtime.

Please take a look at the HP Smart Array Reference Manual and its section on Array Expansion and Migration.

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The old array (4 disks) is a fallback, you are correct. Of course backup will be made & restored to the new array. Objective is space (bigger disks not a possibility since we already have lots of same-size disks). Regarding online expansion, HP strongly suggests to make backups which leads me to think the expansion could fail (what happens if power fails, the genset fails and UPS runs out – it can happen). Also on HP Business Communities it was told it is extremely slow process. I will try this method and reply back the result. Thanks very much for your answer!! –  user1567519 Aug 14 '12 at 3:28
    
These expansions rarely fail. The key is that you have a battery or flash-backed cache unit on your RAID controller (BBWC or FBWC). Without it, the process either won't work or will become unsafe. –  ewwhite Aug 14 '12 at 3:31
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