commit 4c67d0fa1446fef59370f92a5fada4f2f7da375e
parent b6c8eea6e51edea254b385a897279c80741435cb
Author: beau hilton <cbeauhilton@gmail.com>
Date: Thu, 19 Oct 2023 19:29:09 -0500
zfs mirror post
Diffstat:
2 files changed, 138 insertions(+), 0 deletions(-)
diff --git a/index.json b/index.json
@@ -1,5 +1,15 @@
[
{
+ "url": "/posts/add-zfs-mirror",
+ "page_file": "site/posts/add-zfs-mirror.md",
+ "nav_path": [
+ "posts"
+ ],
+ "excerpt": "tl;dr: zpool attach data /dev/disk/by-partlabel/zfs-3a1e459c75dc9b74 /dev/sda1. Adjust for your own pool and disks.",
+ "date": "2023-10-22",
+ "title": "How to add a mirror to a single ZFS disk"
+ },
+ {
"url": "/posts/yt-dlp",
"page_file": "site/posts/yt-dlp.md",
"nav_path": [
diff --git a/site/posts/add-zfs-mirror.md b/site/posts/add-zfs-mirror.md
@@ -0,0 +1,128 @@
+# How to add a mirror to a single ZFS disk
+
+<time id="post-date">2023-10-22</time>
+
+<p id="post-excerpt">
+tl;dr: zpool attach data /dev/disk/by-partlabel/zfs-3a1e459c75dc9b74 /dev/sda1. Adjust for your own pool and disks.
+</p>
+
+
+## A mirror is a Very Good Thing
+
+I got a second identical disk to add as a ZFS mirror to my existing setup.
+
+Redundancy FTW.
+ZFS is king and queen.
+Needs at least two disks to reap the full benefit
+(though a single-disk setup is still rad -
+CoW with snapshots and send/receive are worth it,
+and NixOS makes it easy to set up).
+
+## It's all about the disk path
+
+The basic command is (as a super user, or using sudo):
+
+```sh
+zpool attach name-of-the-pool disk-you-already-had disk-you-want-to-add
+```
+
+On Linux, with a new drive,
+no need for formatting or any other disk preparation.
+Just plug it in.
+
+But how to specify which disks to use in the command?
+I saw several guides that just used `/dev/sdx`, but it didn't work.
+
+In my setup, `/dev/sdb` was my existing drive
+and `/dev/sda` is the one I was trying to add
+(these names are determined at boot time
+and can vary from boot to boot -
+ZFS takes care of finding things again on the back end
+after you've added a drive,
+regardless of the label you used to add it,
+so using the `/dev/sdx` name is just fine in many situations).
+
+However, using
+```sh
+zpool attach data /dev/sdb dev/sda
+```
+
+gave me:
+
+```sh
+cannot attach /dev/sda to /dev/sdb: no such device in pool
+``````
+
+I tried a bunch of different things, from just the lsblk name with the partition ("sdb1"),
+to by-id ("ata-ST1400..."), to full path combinations, etc.
+
+What finally worked was the
+by-partlabel identifier for the existing disk,
+combined with the /dev/sdx0 name of the new one.
+
+A little `zdb -l` on the existing drive gave me the path I wanted:
+
+```sh
+zdb -l /dev/sdb1
+------------------------------------
+LABEL 0
+------------------------------------
+ version: 5000
+ name: 'data'
+ state: 0
+ txg: 170113
+ pool_guid: 8237228336559358688
+ errata: 0
+ hostid: 3236406100
+ hostname: 'dell7050'
+ top_guid: 11182661003591634341
+ guid: 11182661003591634341
+ vdev_children: 1
+ vdev_tree:
+ type: 'disk'
+ id: 0
+ guid: 11182661003591634341
+ path: '/dev/disk/by-partlabel/zfs-3a1e459c75dc9b74'
+ whole_disk: 1
+ metaslab_array: 128
+ metaslab_shift: 34
+ ashift: 12
+ asize: 14000504438784
+ is_log: 0
+ DTL: 3865
+ create_txg: 4
+ features_for_read:
+ com.delphix:hole_birth
+ com.delphix:embedded_data
+ labels = 0 1 2 3
+```
+
+So I tried:
+
+```sh
+zpool attach data /dev/disk/by-partlabel/zfs-3a1e459c75dc9b74 /dev/sda1
+```
+
+## Great success
+
+```sh
+zpool status
+
+ pool: data
+ state: ONLINE
+status: One or more devices is currently being resilvered. The pool will
+ continue to function, possibly in a degraded state.
+action: Wait for the resilver to complete.
+ scan: resilver in progress since Thu Oct 19 17:05:26 2023
+ 2.33T scanned at 1.90G/s, 252G issued at 205M/s, 3.77T total
+ 252G resilvered, 6.53% done, 04:59:42 to go
+config:
+
+ NAME STATE READ WRITE CKSUM
+ data ONLINE 0 0 0
+ mirror-0 ONLINE 0 0 0
+ zfs-3a1e459c75dc9b74 ONLINE 0 0 0
+ sda1 ONLINE 0 0 0 (resilvering)
+
+errors: No known data errors
+```
