1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
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>
|
