Date: Mon, 30 Nov 2009 15:08:35 -0600 From: "James R. Van Artsdalen" <james-freebsd-fs2@jrv.org> To: Zaphod Beeblebrox <zbeeble@gmail.com> Cc: freebsd-fs <freebsd-fs@freebsd.org> Subject: Re: ZFS guidelines - preparing for future storage expansion Message-ID: <4B143453.5090603@jrv.org> In-Reply-To: <5f67a8c40911301233s46a2818at9051c4ebbacf7e25@mail.gmail.com> References: <2ae8edf30911300120x627e42a9ha2cf003e847d4fbd@mail.gmail.com> <4B139AEB.8060900@jrv.org> <2ae8edf30911300425g4026909bm9262f6abcf82ddcd@mail.gmail.com> <5f67a8c40911301233s46a2818at9051c4ebbacf7e25@mail.gmail.com>
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Zaphod Beeblebrox wrote: > I moved from 5x 750G to 5x 1.5T disks this way earlier this year. > [...] And keep in mind that while you're upgrading, you're vulnerable > to data loss (no more replicas). This is one of the (many) reasons I prefer mirrors rather than parity (RAID-5). You can "attach" the new drive, wait for the resilver to complete, then detach the old drive - never having fewer than two drives in the mirror. And of course you can gain space in the pool as each mirror is upgraded whereas a parity group (RAIDZ) usually involves more drives. Note that the zpool(1) man page says of the "Replace" command: "Replaces old_device with new_device. This is equivalent to attaching new_device, waiting for it to resilver, and then detaching old_device". This is not quite true: the reads for the resilver come from all available devices if you do attach/detach, but do not come from old_device if you do "replace". This is for MIRRORs; I'm not sure how RAIDZ behaves.
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