Date: Sat, 19 May 2012 13:13:28 +0300 From: Daniel Kalchev <daniel@digsys.bg> To: freebsd-fs@freebsd.org Subject: Re: Mirror of Raidz for data reliability Message-ID: <4FB77248.50709@digsys.bg> In-Reply-To: <CBDBEF7C.2B265%trent@snakebite.org> References: <CBDBEF7C.2B265%trent@snakebite.org>
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On 18.05.12 19:55, Trent Nelson wrote: > So, my thinking isŠ because both machines can see all disks, the > master could import the zpool as normal, and the slave could import it > read-only. (Or not import it at all...) The proper way of doing it is "not import it at all". ZFS is not an shared filesystem. If you have the second host mount the zpool even if read-only, you only guarantee that data on the pool will not be corrupted, but you cannot avoid the second "read-only" host panic or otherwise crash if it tries to access data which is no longer where it thinks it is, because the second host doesn't have access to the primary host's in-memory metadata about ZFS. Since ZFS is copy on write filesystem, chances are you will be accessing data that is no longer valid. Refreshing the internal ZFS state between two or more hosts is non-trivial (if it was, Sun would have done this, as it suits their usage) and in any case performance will suffer at least as much as an true networked filesystem does, compared to "native" ZFS. Danielhelp
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