Date: Mon, 28 Jan 2013 11:22:30 -0500 From: Paul Kraus <paul@kraus-haus.org> To: FreeBSD Mailing List <freebsd-questions@freebsd.org> Subject: Re: Starting with ZFS on fresh install Message-ID: <4982641D-5691-4CF3-8385-6A836E4AC2A3@kraus-haus.org> In-Reply-To: <201301281539.58864.jmc-freebsd2@milibyte.co.uk> References: <BLU0-SMTP4490AA5B4BAE0C642F7D64593180@phx.gbl> <201301281539.58864.jmc-freebsd2@milibyte.co.uk>
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On Jan 28, 2013, at 10:39 AM, Mike Clarke wrote: > If you're going to be using ZFS then you'll probably be better off not = having=20 > separate partitions and letting ZFS manage space allocation if you = want to=20 > limit the size of /var or any other part of the system, You can manage space within a ZFS pool, regardless of whether you give = the zpool whole disks or a partition. rootpool 6.13G 56.4G 31K none rootpool/do-not-remove 31K 1024M 31K none rootpool/root 5.01G 56.4G 5.01G / rootpool/tmp 60.5K 56.4G 60.5K /tmp rootpool/var 111M 56.4G 111M /var Shows a system with a rootpool and within the rootpool three separate = fielsyetms: / (root) /var /tmp You can control space usage with the zfs quota property. Note the rootpool/do-not-remove daatset. This has a quota and = reservation of 1 GB. It's purpose is to permit recovery in case the = zpool is accidentally filled. ZFS requires *some* free space top process = file / directory remove operations. If the zpool is completely filled = you will NOT be able to remove anything to free up space. By having a = dataset with a quota and reservation of 1 GB, that space is already = marked as used so it will not be allocated. If the remainder of the = zpool fills, then you can quiet the system (so running processes don't = steal the space you are about to free up), change the quota / = reservation (I like going down to 512 MB), and then remove some files / = directories to free up space.=20 Note that the zpool itself (rootpool) is NOT used as a dataset and is = NOT mounted. My experience with ZFS under Solaris taught me that while = you *can* use that dataset, if you have any child datasets (and any = other datasets created will, by definition, be children of the rootpool) = you will end up with hierarchical datasets. This means that future = operations on datasets will have to take place in very specific order = (such as mounting and un mounting). By avoiding hierarchical datasets = (that are actually used) you avoid that complexity. -- Paul Kraus Deputy Technical Director, LoneStarCon 3 Sound Coordinator, Schenectady Light Opera Company
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