SLES系统BtrFS快照的文件系统规划与配置调优问询

我了解到SLES系统采用BtrFS作为根文件系统，还会在系统更新前后自动创建编号快照——要是系统出问题了，还能从旧快照（搭配对应的旧内核）启动，理论上这功能挺贴心的，但实际用起来我碰到了几个具体问题，想请教大家：

• 假设日常系统使用的空间不会超过20GB，那根文件系统该设置多大才合适？
• 如果同时想启用时间线快照，该怎么调整配置才能让快照的磁盘占用保持在可控范围内？

目前我用的snapper配置是这样的（过滤掉了注释行）：

grep '^[^#]' /etc/snapper/configs/root

输出内容：

SUBVOLUME="/"
FSTYPE="btrfs"
QGROUP="1/0"
SPACE_LIMIT="0.5"
FREE_LIMIT="0.2"
ALLOW_USERS=""
ALLOW_GROUPS=""
SYNC_ACL="no"
BACKGROUND_COMPARISON="yes"
NUMBER_CLEANUP="yes"
NUMBER_MIN_AGE="1800"
NUMBER_LIMIT="2-10"
NUMBER_LIMIT_IMPORTANT="4-10"
TIMELINE_CREATE="yes"
TIMELINE_CLEANUP="yes"
TIMELINE_MIN_AGE="1800"
TIMELINE_LIMIT_HOURLY="10"
TIMELINE_LIMIT_DAILY="5"
TIMELINE_LIMIT_WEEKLY="3"
TIMELINE_LIMIT_MONTHLY="3"
TIMELINE_LIMIT_YEARLY="2"
EMPTY_PRE_POST_CLEANUP="yes"
EMPTY_PRE_POST_MIN_AGE="1800"

我的核心需求是：希望能预留计划磁盘空间的50%给快照，针对这个需求，该怎么调整上面的配置参数呢？

另外附上我当前系统里的快照列表（后续大概率还会增加）：

snapper list

输出内容：

# | Type   | Pre # | Date                     | User | Used Space | Cleanup  | Description              | Userdata
------+--------+-------+--------------------------+------+------------+----------+--------------------------+--------------
0  | single |       |                          | root |            |          | current                  |
1* | single |       | Tue Jan 24 12:35:33 2023 | root | 144.00 KiB |          | first root filesystem    |
27  | single |       | Thu Jan 26 10:14:39 2023 | root | 325.28 MiB |          | Installation DP CM 11.02 |
42  | single |       | Thu Feb  2 14:00:01 2023 | root | 492.13 MiB | timeline | timeline                 |
5181  | single |       | Fri Sep  1 00:00:01 2023 | root | 172.21 MiB | timeline | timeline                 |
5274  | pre    |       | Mon Sep  4 11:26:42 2023 | root | 102.06 MiB | number   | zypp(ruby.ruby2.5)       | important=yes
5275  | post   |  5274 | Mon Sep  4 11:29:41 2023 | root | 194.42 MiB | number   |                          | important=yes
5917  | single |       | Sun Oct  1 00:00:01 2023 | root |  13.92 MiB | timeline | timeline                 |
6172  | pre    |       | Wed Oct 11 14:51:34 2023 | root |   1.23 MiB | number   | yast online_update       |
6175  | pre    |       | Wed Oct 11 14:53:16 2023 | root |  97.12 MiB | number   | zypp(ruby.ruby2.5)       | important=yes
6176  | post   |  6175 | Wed Oct 11 14:56:43 2023 | root | 304.00 KiB | number   |                          | important=yes
6177  | post   |  6172 | Wed Oct 11 14:56:54 2023 | root | 256.00 KiB | number   |                          |
6178  | pre    |       | Wed Oct 11 14:58:37 2023 | root | 928.00 KiB | number   | zypp(zypper)             | important=yes
6179  | post   |  6178 | Wed Oct 11 14:58:47 2023 | root |   1.30 MiB | number   |                          | important=yes
6621  | single |       | Mon Oct 30 00:00:01 2023 | root |   6.52 MiB | timeline | timeline                 |
6669  | single |       | Wed Nov  1 00:00:01 2023 | root |   6.50 MiB | timeline | timeline                 |
6789  | single |       | Mon Nov  6 00:00:01 2023 | root |   6.47 MiB | timeline | timeline                 |
6933  | single |       | Sun Nov 12 00:00:01 2023 | root |   6.20 MiB | timeline | timeline                 |
6957  | single |       | Mon Nov 13 00:00:01 2023 | root |   5.84 MiB | timeline | timeline                 |
6981  | single |       | Tue Nov 14 00:00:01 2023 | root |   3.48 MiB | timeline | timeline                 |
7005  | single |       | Wed Nov 15 00:00:01 2023 | root |   2.91 MiB | timeline | timeline                 |
7029  | single |       | Thu Nov 16 00:00:01 2023 | root | 464.00 KiB | timeline | timeline                 |
7032  | single |       | Thu Nov 16 03:00:01 2023 | root |  16.00 KiB | timeline | timeline                 |
7033  | single |       | Thu Nov 16 04:00:01 2023 | root |  16.00 KiB | timeline | timeline                 |
7034  | single |       | Thu Nov 16 05:00:01 2023 | root |  64.00 KiB | timeline | timeline                 |
7035  | single |       | Thu Nov 16 06:00:01 2023 | root |  16.00 KiB | timeline | timeline                 |
7036  | single |       | Thu Nov 16 07:00:01 2023 | root |  16.00 KiB | timeline | timeline                 |
7037  | single |       | Thu Nov 16 08:00:01 2023 | root |  32.00 KiB | timeline | timeline                 |
7038  | single |       | Thu Nov 16 09:00:01 2023 | root |  80.00 KiB | timeline | timeline                 |
7039  | single |       | Thu Nov 16 10:00:01 2023 | root | 128.00 KiB | timeline | timeline                 |
7040  | single |       | Thu Nov 16 11:00:01 2023 | root | 272.00 KiB | timeline | timeline                 |
7041  | pre    |       | Thu Nov 16 11:50:58 2023 | root | 512.00 KiB | number   | yast online_update       |
7042  | pre    |       | Thu Nov 16 11:52:45 2023 | root |   1.27 MiB | number   | zypp(ruby.ruby2.5)       | important=yes
7043  | post   |  7042 | Thu Nov 16 11:56:35 2023 | root | 560.00 KiB | number   |                          | important=yes
7044  | post   |  7041 | Thu Nov 16 11:56:42 2023 | root | 464.00 KiB | number   |                          |
7045  | pre    |       | Thu Nov 16 11:58:15 2023 | root | 768.00 KiB | number   | zypp(zypper)             | important=yes
7046  | post   |  7045 | Thu Nov 16 11:58:27 2023 | root | 320.00 KiB | number   |                          | important=yes
7047  | single |       | Thu Nov 16 12:00:01 2023 | root | 176.00 KiB | timeline | timeline                 |
7048  | single |       | Thu Nov 16 13:00:01 2023 | root |  32.00 KiB | timeline | timeline                 |

备注：内容来源于stack exchange，提问作者U. Windl