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I have two older PCs on my LAN posing as 'servers'; one running FreeNAS off a USB stick using three 500GB HDDs in a ZFS RAID-Z pool serving as storage for the LAN and one running Debian Lenny with an 80GB drive used as a general purpose 'tinker' box that I can ssh into, etc. Problem is that the SMART report for one of those 500GB drives in the FreeNAS box is showing some pre-failure attributes, and the whole array is a little small anyways. Rather than simply replace one 500GB drive with another 500GB drive, and have no backup of the file server, I'd like to upgrade all the drives to 2TB ones - but I have no where to store that much data in the mean while. As such, I started looking at getting a 4-bay external drive enclosure with an eSATA card for the Debian box, with the hopes of creating a RAID5 + LVM setup using those drives and backing the data up to that external drive enclosure. After the backup is done, replace the drives in the FreeNAS box and rebuild the array there and mirror the data back. Then, I'd have both the primary storage (on the FreeNAS box) and a backup (which I don't have currently) using the external drive enclosure on the Debian box.

My big question is... most of these external drive boxes seem to claim support for JBOD, RAID 0, 1, 10, 5, etc. - should I presume that is simply fake RAID like many commodity mobos have, and not really usable in Linux? In that case, with all the drives hanging off the one eSATA connection, will Linux (specifically Debian Squeeze, as I plan on upgrading that box here shortly) see all four drives, or just the first one? Will I be able to configure them in a RAID5 array as desired?

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If you get your hands on a QNAP or Drobo box, it's sort of like FreeNAS in that it'll be recognised as a RAID device (assuming you set it up correctly) and it'll be seen as one drive. As for whether it'll work, well I guess it depends on which one you're looking at. –  user3463 Jan 15 '11 at 5:47

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up vote 2 down vote accepted

Did you know you can use a zpool replace command to replace the 500GB drives one at a time with the 2TB drives? If the zpool property autoexpand is set to on when you replace the last drive, the pool will automatically expand to use all the new capacity.

This doesn't require any downtime of your server (besides the powering down to connect drives) and maintains full redundancy.

All the external consumer-level NAS use software RAID, they are usually based on Linux kernels, so they use MDADM. Some, like the Drobo, use a custom software RAID implementation. If you configure these devices to use their HDDs in a RAID then they will only present as a single drive to any client OS.

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What level/version of ZFS is required to support zpool replace? Does it need to be something newer like in OpenSolaris or would the rather older version in FreeNAS support it as well? –  memilanuk Feb 3 '11 at 0:15
    
I'm not sure of the exact version, but here is someone using it on FreeNAS 0.7: corvettekenny.com/freenas/index.php#3 it looks like you have to export and import in order for the VDev to expand on FreeNAS though. –  Hydaral Feb 3 '11 at 5:33
    
Thanks, I'll have to give it a try - definitely doing a 'dry run' first inside a virtual machine, though. –  memilanuk Feb 3 '11 at 18:04

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