Here is a WEIRD one.
Why would one drbd volume be trimmable and the other one not?
Here you can see me issuing the trim command against two different filesystems.
It works on one but fails on the other.
ha11a:~ # fstrim -v /ha01_mysql
/ha01_mysql: 0 B (0 bytes) trimmed
ha11a:~ # fstrim -v /ha02_mysql
fstrim: /ha02_mysql: the discard operation is not supported
Both filesystems are on the same server, two different drbd devices on two
different mdraid arrays, but the same underlying physical drives.
Yet it can be seen that discard is enabled on drbd0 but not on drbd1...
NAME DISC-ALN DISC-GRAN DISC-MAX DISC-ZERO
sda 0 512B 4G 1
├─sda1 0 512B 4G 1
│ └─md0 0 128K 256M 0
├─sda2 0 512B 4G 1
│ └─md1 0 128K 256M 0
├─sda3 0 512B 4G 1
├─sda4 0 512B 4G 1
├─sda5 0 512B 4G 1
│ └─md2 0 1M 256M 0
│ └─drbd0 0 1M 128M 0
│ └─vg_on_drbd0-lv_on_drbd0 393216 1M 128M 0
└─sda6 0 512B 4G 1
└─md3 0 1M 256M 0
└─drbd1 0 0B 0B 0
└─vg_on_drbd1-lv_on_drbd1 0 0B 0B 0
The filesystems are set up the same. (Note that I do not want automatic discard
so that option is not enabled on either filesystem, but the problem is not the
filesystem, since that relies on drbd, and you can see from lsblk that the drbd
volume is the problem.)
ha11a:~ # mount|grep drbd
/dev/mapper/vg_on_drbd1-lv_on_drbd1 on /ha02_mysql type ext4
(rw,relatime,stripe=160,data=ordered)
/dev/mapper/vg_on_drbd0-lv_on_drbd0 on /ha01_mysql type ext4
(rw,relatime,stripe=160,data=ordered)
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