Date: Thu, 26 Mar 2020 16:37:58 -0400 (EDT) From: Daniel Feenberg <feenberg@nber.org> To: Bob Proulx <bob@proulx.com> Cc: freebsd-questions@freebsd.org Subject: Re: drive selection for disk arrays Message-ID: <alpine.BSF.2.21.9999.2003261630030.47777@mail2.nber.org> In-Reply-To: <20200326124648725158537@bob.proulx.com> References: <20200325081814.GK35528@mithril.foucry.net> <713db821-8f69-b41a-75b7-a412a0824c43@holgerdanske.com> <20200326124648725158537@bob.proulx.com>
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The disturbing frequency of multiple drives going offline in quick succession is, in my view, largely a result of defects being discovered in quick succession, rather than occuring in quick succession. If a defect occurs in a sector that is rarely visited it can remain hidden for a long time. During a resilver that defect will be noticed and the drive failed out. I do think that is an overly aggressive action by the resilvering process, as that may be the only bad sector, it may be possible to recover all the data from the remaining drives (if the first failing drive can read the appropriate sector), and that sector may not even be in an active file. This issue makes scrubbing particularly important, especially in this era of very large filesystems that can take days or weeks to restore.
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