Date: Wed, 13 May 2015 09:49:43 -0500 From: Brandon Wandersee <brandon.wandersee@zoho.com> To: freebsd-questions@freebsd.org Subject: Re: ZFS stripe to raidz1 Message-ID: <20150513144943.GA3810@WorkBox.Home> In-Reply-To: <555350E0.5060705@gmail.com> References: <8F1341A6-AA91-418D-97EA-FF7F8AC07F6A@jensenwaud.com> <555350E0.5060705@gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On 05/13, Johan Hendriks wrote: > > You can start with two disks and create a stripe accross both disks. > Keep in mind that if one fails you will loose all your data! > Later on you can mirror disk one by *attaching* a disk to this vdev. But > this way you still have no redundancy. If the second disk/vdev fails, > you still loose all data. You need to *attach* a second disk to the > second vdev also. That way you can loose a disk per mirrored vdev. So > you will need 4 disks. > > regards Just to elaborate a bit on this (for clarity's sake), not only can ZFS not do what you'd like, but plain-old RAID can't either. In order to create a RAID array you'd need to mirror one disk to another: the data layout on one disk is created in a 100% identical manner on the second disk. Because of this, the storage capacity of the array is limited to that of the smallest of the two disks. If you tried to create a RAID array between a 4Tb stripe and a 2Tb disk, you wouldn't get a 4Tb RAID array, but a 2Tb one (leaving one disk unused), and (at least in the case of traditional RAID) the process of creating it would wipe data on the 4Tb stripe anyway. I believe ZFS can create mirrors on live systems without wiping data, but as John said the ideal (though more expensive) track is to start with a stripe and add another *two-disk* stripe later to mirror the first. Or start with RAID1, add a second two-disk RAID1 array later, back up all data and stripe a new filesystem across the two RAID arrays. -- "A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools." - Douglas Adams
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20150513144943.GA3810>