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I am in the process of planning a file server for private usage (small amounts of various kinds of data, but mainly photos, videos, music). I will probably use NAS4free/FreeNAS and want to give ZFS a try.
My focus is not speed, it is reliability and data safety. Nevertheless, I want to keep things 'cheap', so I want to run ZFS mirrored among two disks ('raid 1' fashion). I will buy a consumer board, so no hardware raid controller. So far, I am thinking to use the ZFS 'mirror' command for this or whatever corresponding option FreeNAS provides.
When reading about this topic, I mainly see people using three disks and then using RAIDZ-1 which renders them immune in case one disk fails. What I do not quite understand so far is what is the problem with having ZFS mirrored among two disks only? How will I notice when one disk fails? What is the failover strategy? Do I just get a message that the file system is not usable, because disk A is failing and that I should replace it now? I hope that one can achieve a real benefit when running two mirrored disks than just using one.
Given two equivalent disks, which ZFS mode would you run in?
2"With raidz, you need at least three drives." -- Not true for raidz (single parity). Per the ZFS docs, "You need at least two disks for a single-parity RAID-Z configuration and at least three disks for a double-parity RAID-Z configuration." – Poulsbo – 2015-06-19T17:03:30.000
Thanks for clarification. So with RAIDZ incorporating three drives, there is a net capacity larger than one of the drives has, yes? Would it be two disk sizes in this case? – Jan-Philip Gehrcke – 2013-07-22T19:38:34.023
@Jan-PhilipGehrcke Yes. Assuming the drives are all the same size, a mirror array has the same usable size as 1 drive (no matter how many disks you use), whereas RAIDZ has N-1 drives of usable space. (Three drives gives you two drives of usable space, five drives gives you 4 drives of usable space, etc.). – Darth Android – 2013-07-22T22:09:13.723