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diff --git a/drafts/expanding-zroot-mirrored-vdevs.html b/drafts/expanding-zroot-mirrored-vdevs.html new file mode 100644 index 0000000..e15f262 --- /dev/null +++ b/drafts/expanding-zroot-mirrored-vdevs.html @@ -0,0 +1,299 @@ +<h1>Root on ZFS: A ZPool of Mirror VDEVs</h1> + +<p class="description"> + I wanted/needed to make a root on ZFS pool out of multiple mirror VDEVs, and + since I'm not a ZFS expert, I took a little shortcut. +</p> + +<p> + I recently got a new-to-me server (yay!) and I wanted to do a root-on-ZFS + setup on it. I've really enjoyed using ZFS for my data storage pools for a + long time. I've also enjoyed the extra functionality that comes with having a + bootable system installed on ZFS on my laptop and decided with this upgrade + it's time to do the same on my server. Historically I've used RAIDZ for my + storage pools. RAIDZ functions almost like a RAID10 but at the ZFS level. It + gives you parity so that a certain number of disks can die from your pool and + you won't lose any data. It does have a few tradeoffs however*, and for + personal preferences I've decided that for the future I would like to have a + single ZPool over top of multiple mirror VDEVs. In other words, my main + root+storage pool will be made up of two-disk mirrors and can be expanded to + include any number of new mirrors I can fit into the machine. +</p> + +<p> + This did present some complications. First of all, + <code>bsdinstall</code> won't set this up for you automatically (and sure + enough, + <a href="https://www.freebsd.org/doc/handbook/bsdinstall-partitioning.html" + >in the handbook</a + > + it mentions the guided root on ZFS tool will only create a single, top-level + VDEV unless it's a stripe). It will happily let you use RAIDZ for your ZROOT + but not the more custom approach I'm taking. I did however use + <code>bsdinstall</code> as a shortcut so I wouldn't have to do all of the + partitioning and pool setup manually, and that's what I'm going to document + below. Because I'm totally going to forget how this works the next time I have + to do it. +</p> + +<p> + In my scenario I have an eight-slot, hot-swappable PERC H310 controller that's + configured for AHCI passthrough. In other words, all FreeBSD sees is as many + disks as I have plugged into the backplane. I'm going to fill it with 6x2TB + hard disks which, as I said before, I want to act as three mirrors (two disks + each) in a single, bootable, growable ZPool. For starters, I shoved the + FreeBSD installer on a flash drive and booted from it. I followed all of the + regular steps (setting hostname, getting online, etc.) until I got to the + guided root on ZFS disk partitioning setup. +</p> + +<p> + Now here's where I'm going to take the first step on my shortcut. Since there + is no option to create the pool of arbitrary mirrors I'm just going to create + a pool from a single mirror VDEV of two disks. Later I will expand the pool to + include the other two mirrors I had intended for. My selections were as + follows: +</p> + +<ul> + <li>Pool Type/Disks: mirror mfisyspd0 mfisyspd1</li> + <li>Pool Name: zroot</li> + <li>Partition Scheme: GPT (EFI)</li> + <li>Swap Size: 4g</li> +</ul> + +<p> + Everything else was left as a default. Then I followed the installer to + completion. At the end, when it asked if I wanted to drop into a shell to do + more to the installation, I did. +</p> + +<p> + The installer created the following disk layout for the two disks that I + selected. +</p> + +<pre> +<code> +atc@macon:~ % gpart show +=> 40 3907029088 mfisyspd0 GPT (1.8T) + 40 409600 1 efi (200M) + 409640 2008 - free - (1.0M) + 411648 8388608 2 freebsd-swap (4.0G) + 8800256 3898228736 3 freebsd-zfs (1.8T) + 3907028992 136 - free - (68K) + +=> 40 3907029088 mfisyspd1 GPT (1.8T) + 40 409600 1 efi (200M) + 409640 2008 - free - (1.0M) + 411648 8388608 2 freebsd-swap (4.0G) + 8800256 3898228736 3 freebsd-zfs (1.8T) + 3907028992 136 - free - (68K) +</code> +</pre> + +<p> + The installer also created the following ZPool from my single mirror VDEV. +</p> + +<pre> +<code> +atc@macon:~ % zpool status + pool: zroot + state: ONLINE + scan: none requested +config: + + NAME STATE READ WRITE CKSUM + zroot ONLINE 0 0 0 + mirror-0 ONLINE 0 0 0 + mfisyspd0p3 ONLINE 0 0 0 + mfisyspd1p3 ONLINE 0 0 0 + +errors: No known data errors +</code> +</pre> + +<p> + There are a couple of things to take note of here. First of all, + <em>both</em> disks in the bootable ZPool have an EFI boot partition. That + means they're both a part of (or capable of?) booting the pool. Second, they + both have some swap space. Finally, they both have a third partition which is + dedicated to ZFS data, and that partition is what got added to my VDEV. +</p> + +<p> + So where do I go from here? I was tempted to just + <code>zpool add mirror ... ...</code> and just add my other disks to the pool + (actually, I <em>did</em> do this but it rendered the volume unbootable for a + very important reason), but then I wouldn't have those all-important boot + partitions (using whole-disk mirror VDEVS). Instead, I need to manually go + back and re-partition four disks exactly like the first two. Or, since all I + want is two more of what's already been done, I can just clone the partitions + using <code>gpart backup</code> and <code>restore</code>! Easy! Here's what I + did for all four remaining disks: +</p> + +<pre> +<code> +root@macon:~ # gpart backup mfisyspd0 | gpart restore -F mfisyspd2` +</code> +</pre> + +<p> + Full disclosure, I didn't even think of this as a possibility + <a + href="ihttps://unix.stackexchange.com/questions/472147/replacing-disk-when-using-freebsd-zfs-zroot-zfs-on-partition#472175" + >until I read this Stack Exchange post</a + >. This gave me a disk layout like this: +</p> + +<pre> +<code> +atc@macon:~ % gpart show +=> 40 3907029088 mfisyspd0 GPT (1.8T) + 40 409600 1 efi (200M) + 409640 2008 - free - (1.0M) + 411648 8388608 2 freebsd-swap (4.0G) + 8800256 3898228736 3 freebsd-zfs (1.8T) + 3907028992 136 - free - (68K) + +=> 40 3907029088 mfisyspd1 GPT (1.8T) + 40 409600 1 efi (200M) + 409640 2008 - free - (1.0M) + 411648 8388608 2 freebsd-swap (4.0G) + 8800256 3898228736 3 freebsd-zfs (1.8T) + 3907028992 136 - free - (68K) + +=> 40 3907029088 mfisyspd2 GPT (1.8T) + 40 409600 1 efi (200M) + 409640 2008 - free - (1.0M) + 411648 8388608 2 freebsd-swap (4.0G) + 8800256 3898228736 3 freebsd-zfs (1.8T) + 3907028992 136 - free - (68K) + +=> 40 3907029088 mfisyspd3 GPT (1.8T) + 40 409600 1 efi (200M) + 409640 2008 - free - (1.0M) + 411648 8388608 2 freebsd-swap (4.0G) + 8800256 3898228736 3 freebsd-zfs (1.8T) + 3907028992 136 - free - (68K) + +=> 40 3907029088 mfisyspd4 GPT (1.8T) + 40 409600 1 efi (200M) + 409640 2008 - free - (1.0M) + 411648 8388608 2 freebsd-swap (4.0G) + 8800256 3898228736 3 freebsd-zfs (1.8T) + 3907028992 136 - free - (68K) + +=> 40 3907029088 mfisyspd5 GPT (1.8T) + 40 409600 1 efi (200M) + 409640 2008 - free - (1.0M) + 411648 8388608 2 freebsd-swap (4.0G) + 8800256 3898228736 3 freebsd-zfs (1.8T) + 3907028992 136 - free - (68K) +</code> +</pre> + +<p> + And to be fair, this makes a lot of logical sense. You don't want a six-disk + pool to only be bootable by two of the disks or you're defeating some of the + purposes of redundancy. So now I can extend my ZPool to include those last + four disks. +</p> + +<p> + This next step may or may not be a requirement. I wanted to overwrite where I + assumed any old ZFS/ZPool metadata might be on my four new disks. This could + just be for nothing and I admit that, but I've run into trouble in the past + where a ZPool wasn't properly exported/destroyed before the drives were + removed for another purpose and when you use those drives in future + <code>zpool import</code>s, you can see both the new and the old, failed + pools. And, in the previous step I cloned an old ZFS partition many times! So + I did a small <code>dd</code> on the remaining disks to help me sleep at + night: +</p> + +<pre> +<code> +root@macon:~ # dd if=/dev/zero of=/dev/mfisyspd2 bs=1M count=100 +</code> +</pre> + +<p> + One final, precautionary step is to write the EFI boot loader to the new + disks. In + <a href="https://www.freebsd.org/doc/handbook/zfs-zpool.html" + >zpool admin handbook</a + > + it mentions you should do this any time you <em>replace</em> a zroot device, + so I'll do it just for safe measure on all four additional disks: +</p> + +<pre> +<code> +root@macon:~ # gpart bootcode -p /boot/boot1.efifat -i 1 mfisyspd2 +</code> +</pre> + +<p> + Don't forget that the command is different for UEFI and a traditional BIOS. + And finally, I can add my new VDEVs: +</p> + +<pre> +<code> +root@macon:~ # zpool zroot add mirror mfisyspd2p3 mfisyspd3p3 +root@macon:~ # zpool zroot add mirror mfisyspd4p3 mfisyspd5p3 +</code> +</pre> + +<p>And now my pool looks like this:</p> + +<pre> +<code> +atc@macon:~ % zpool status + pool: zroot + state: ONLINE + scan: none requested +config: + + NAME STATE READ WRITE CKSUM + zroot ONLINE 0 0 0 + mirror-0 ONLINE 0 0 0 + mfisyspd0p3 ONLINE 0 0 0 + mfisyspd1p3 ONLINE 0 0 0 + mirror-1 ONLINE 0 0 0 + mfisyspd2p3 ONLINE 0 0 0 + mfisyspd3p3 ONLINE 0 0 0 + mirror-2 ONLINE 0 0 0 + mfisyspd4p3 ONLINE 0 0 0 + mfisyspd5p3 ONLINE 0 0 0 + +errors: No known data errors +</code> +</pre> + +<p> + Boom. A growable, bootable zroot ZPool. Is it easier than just configuring the + partitions and root on ZFS by hand? Probably not for a BSD veteran. But since + I'm a BSD layman, this is something I can live with pretty easily. At least + until this becomes an option in <code>bsdintall</code> maybe? At least now I + can add as many more mirrors as I can fit into my system. And it's just as + easy to replace them. This is better for me than my previous RAIDZ, where I + would have to destroy and re-create the pool in order to add more disks to the + VDEV. Now I just create another little mirror and grow the pool and all of my + filesystems just see more storage. And of course, having ZFS for all of my + data makes it super easy to create filesystems on the fly, compress or quota + them, and take snapshots (including the live ZROOT!) and send those snapshots + over the network. Pretty awesome. +</p> + +<p> + * I'm not going to explain why here, but + <a href="http://www.openoid.net/zfs-you-should-use-mirror-vdevs-not-raidz/" + >this is a pretty well thought out article</a + > + that should give you an idea about the pros and cons of RAIDZ versus mirror + VDEVs so you can draw your own conclusions. +</p> |