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> That isn't my understanding as far as raidz reshaping goes. You can |
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> create raidz's and add them to a zpool. You can add individual |
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> drives/partitions to zpools. You can remove any of these from a zpool |
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> at any time and have it move data into other storage areas. However, |
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> you can't reshape a raidz. |
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|
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ZFS is organized into pools, which are transactional object stores. |
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Various things can go into these transactional object stores, such as |
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ZFS data sets and zvols. A ZFS data set is what you would consider to |
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be a filesystem. A zvol is a block device on which other filesystems |
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can be installed. Data in pools are stored in vdevs, which can be |
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files masquerading as block devices, single disks, mirrored disks or a |
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raidz level. |
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|
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ZFS is designed to put data integrity first. I question how many other |
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volume managers are capable of recovering from a crash during a |
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reshape without some sort of catastrophic data loss. WIth that said, I |
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do not see what your point is to talk about this. There are things you |
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can use your extra disk to do, but as far as storage requirements go, |
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a single disk does not go very far. You are better off replacing |
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hardware if your storage requirements grow beyond the ability of your |
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current disks to handle. |
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|
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> Suppose I have a system with 5x1TB hard drives. They're merged into a |
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> single raidz with single-parity, so I have 4TB of space. I want to |
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> add one 1TB drive to the array and have 5TB of single-parity storage. |
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> As far as I'm aware you can't do that with raidz. What you could do |
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> is set up some other 4TB storage area (raidz or otherwise), remove the |
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> original raidz, recycle those drives into the new raidz, and then move |
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> the data back onto it. However, doing this requires 4TB of storage |
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> space. With mdadm you could do this online without the need for |
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> additional space as a holding area. |
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|
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If you have proper backups, you should be able to destroy the pool, |
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make a new one and restore the backup. If you do not have backups, |
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then I think there are more important things to consider than your |
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ability to do this without them. |
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|
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> ZFS is obviously a capable filesystem, but unless Oracle re-licenses |
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> it we'll never see it take off on Linux. For good or bad everybody |
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> seems to like the monolithic kernel. Btrfs obviously has a ways to go |
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> before it is a viable replacement, but I doubt Oracle would be sinking |
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> so much money into it if they intended to ever re-license ZFS. |
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|
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I heard a statement in IRC that Oracle owns all of the next generation |
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filesystems, which enables them to position btrfs for the low-end and |
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use ZFS at the high-end. I have no way of substantiating this, but I |
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can say that this does appear to be the case. |
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|
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With that said, ebuilds are in the portage tree and support has been |
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integrated into genkernel. I have a physical system booting off ZFS |
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(no ext4 et al) and genkernel makes kernel upgrades incredibly easy, |
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even when configuring my own kernel through --menuconfig. Gentoo users |
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in IRC are quite interested in this and they do not seem to care that |
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the modules are out-of-tree or that the licensing is different. As far |
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as I can tell, there is no need for them to care. |
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|
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You might want to look at Gentoo/FreeBSD, which also supports ZFS with |
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a monolithic kernel design, but has no licensing issues. There is |
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nothing forcing any of us to use Linux and if the licensing is a |
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problem for you, then perhaps it would be a good idea to switch. |
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|
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Also, to avoid any confusion, a proper bootloader for ZFS does not |
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exist in portage at this time. I hacked the boot process to enable the |
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system to boot off ZFS using GRUB and it will require some more work |
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before this is ready for inclusion into portage. I made an |
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announcement to the ZFSOnLinux mailing list not that long ago |
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explaining what I did. I was waiting until ZFS support in Gentoo |
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reached a few milestones before I made an announcement about it here, |
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although most of the stuff you need is already in-tree: |
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|
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http://groups.google.com/a/zfsonlinux.org/group/zfs-discuss/browse_thread/thread/d94f597f8f4e3c88 |