Date: Mon, 13 Feb 2012 18:45:20 +0200 From: Andriy Gapon <avg@FreeBSD.org> To: Kevin Day <toasty@dragondata.com> Cc: freebsd-fs@FreeBSD.org Subject: Re: Simultaneous read-only snapshot mount Message-ID: <4F393E20.3070308@FreeBSD.org> In-Reply-To: <A14E351F-9C8C-4239-9ECD-E84F3BBFD9D5@dragondata.com> References: <A14E351F-9C8C-4239-9ECD-E84F3BBFD9D5@dragondata.com>
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on 13/02/2012 17:55 Kevin Day said the following: > > It's now possible/somewhat common for the ability to have two systems can see > the same disk(s) at the same time (through iSCSI or storage systems that > support dual controllers, etc). > > Suppose system A has a filesystem mounted RW, and takes a snapshot. Can system > B access that snapshot via a read only mount, while system A continues to > read/write to that filesystem? Or more basically, is everything needed to read > a snapshot stable/unchanging enough that a second system can read from it while > the filesystem is still being updated? Generally, no. The RO fs typically still caches a lot of information (metadata) in RAM, the cached data may become stale and inconsistent. -- Andriy Gapon
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