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I'm considering using FreeNAS and "recycling" some of my older 1TB disks. Two are the exact same model Western Digital while another is Seagate and the fourth is Samsung.

Typically, since all disks are not equal, I'll create my arrays on a Windows-based server 1GB undersized to prevent a replacement disk not being large enough. Dell is notorious for sending replacement SATA disks of different brand---knock on wood, no problems yet.

Since not all drives are created equally and they can vary a few MBs, is there a way to make the the FreeNas/ZFS/Raid-Z function in the same way I do for my Windows-based servers above?


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Recent ZFS version do allow some slack when it comes to slightly different drive sizes. Basically, when you create ZFS pool ZFS leaves some spare space on the slice unused, so if some time later you replace a drive with a slightly smaller one, the smaller drive would still be accepted, though it will have smaller unused chunk on it.

As an alternative, you can do this explicitly and build ZFS pool from partitions sized to be a bit smaller that the drives you use. If you get a smaller drive later, as long as it can still accommodate your partition size, there will be no trouble.

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