On Sun, 29 Jul 2018 1:13 am Eric Robinson <eric.robin...@psmnv.com> wrote:
> > > > > > -----Original Message----- > > From: Eric Robinson > > Sent: Saturday, July 28, 2018 7:39 AM > > To: Lars Ellenberg <lars.ellenb...@linbit.com>; > drbd-user@lists.linbit.com > > Subject: RE: [DRBD-user] drbd+lvm no bueno > > > > > > > Lars, > > > > > > > > > > I put MySQL databases on the drbd volume. To back them up, I pause > > > > > them and do LVM snapshots (then rsync the snapshots to an archive > > > > > server). How could I do that with LVM below drbd, since what I > > > > > want is a snapshot of the filesystem where MySQL lives? > > > > > > > > You just snapshot below DRBD, after "quiescen" the mysql db. > > > > > > > > DRBD is transparent, the "garbage" (to the filesystem) of the > > > > "trailing drbd meta data" is of no concern. > > > > You may have to "mount -t ext4" (or xfs or whatever), if your mount > > > > and libblkid decide that this was a "drbd" type and could not be > > > > mounted. They are just trying to help, really. > > > > which is good. but in that case they get it wrong. > > > > > > Okay, just so I understand.... > > > > > > Suppose I turn md4 into a PV and create one volume group > > > 'vg_under_drbd0', and logical volume 'lv_under_drbd0' that takes 95% > > > of the space, leaving 5% for snapshots. > > > > > > Then I create my ext4 filesystem directly on drbd0. > > > > > > At backup time, I quiesce the MySQL instances and create a snapshot of > > > the drbd disk. > > > > > > I can then mount the drbd snapshot as a filesystem? > > > > > > > Disregard question. I tested it. Works fine. Mind blown. > > > > -Eric > > > > Although I discovered quite by accident that you can mount a snapshot over > the top of the filesystem that exists on the device that it's a snapshot > of. Wouldn't this create some sort of recursive write death spiral? > I think this can help properly understanding lvm snapshots and answer your question https://www.clevernetsystems.com/lvm-snapshots-explained/ > Check it out... > > root@001db01a /]# lvdisplay > --- Logical volume --- > LV Path /dev/vg_under_drbd1/lv_under_drbd1 > LV Name lv_under_drbd1 > VG Name vg_under_drbd1 > LV UUID LWWPiL-Y6nR-cNnW-j2E9-LAK9-UsXm-3inTyJ > LV Write Access read/write > LV Creation host, time 001db01a, 2018-07-28 04:53:14 +0000 > LV Status available > # open 2 > LV Size 1.40 TiB > Current LE 367002 > Segments 1 > Allocation inherit > Read ahead sectors auto > - currently set to 8192 > Block device 253:1 > > --- Logical volume --- > LV Path /dev/vg_under_drbd0/lv_under_drbd0 > LV Name lv_under_drbd0 > VG Name vg_under_drbd0 > LV UUID M2oMNd-hots-d9Pf-KQG8-YPqh-6x3a-r6wBqo > LV Write Access read/write > LV Creation host, time 001db01a, 2018-07-28 04:52:59 +0000 > LV Status available > # open 2 > LV Size 1.40 TiB > Current LE 367002 > Segments 1 > Allocation inherit > Read ahead sectors auto > - currently set to 8192 > Block device 253:0 > > [root@001db01a /]# df -h > Filesystem Size Used Avail Use% Mounted on > /dev/sda2 30G 3.3G 27G 12% / > devtmpfs 63G 0 63G 0% /dev > tmpfs 63G 0 63G 0% /dev/shm > tmpfs 63G 9.0M 63G 1% /run > tmpfs 63G 0 63G 0% /sys/fs/cgroup > /dev/sda1 497M 78M 420M 16% /boot > /dev/sdb1 252G 61M 239G 1% /mnt/resource > tmpfs 13G 0 13G 0% /run/user/0 > /dev/drbd0 1.4T 2.1G 1.4T 1% /ha01_mysql > [root@001db01a /]# > [root@001db01a /]# ls /ha01_mysql > lost+found testfile > [root@001db01a /]# > [root@001db01a /]# lvcreate -s -L30G -n drbd0_snapshot > /dev/vg_under_drbd0/lv_under_drbd0 > Logical volume "drbd0_snapshot" created. > [root@001db01a /]# > [root@001db01a /]# mount /dev/vg_under_drbd0/drbd0_snapshot /ha01_mysql > [root@001db01a /]# > [root@001db01a /]# cd /ha01_mysql > [root@001db01a ha01_mysql]# ls > lost+found testfile > [root@001db01a ha01_mysql]# echo blah > blah.txt > [root@001db01a ha01_mysql]# ll > total 2097172 > -rw-r--r--. 1 root root 5 Jul 28 14:50 blah.txt > drwx------. 2 root root 16384 Jul 28 14:10 lost+found > -rw-r--r--. 1 root root 2147479552 Jul 28 14:20 testfile > [root@001db01a ha01_mysql]# cd / > [root@001db01a /]# umount /ha01_mysql > [root@001db01a /]# ls /ha01_mysql > lost+found testfile > [root@001db01a /]# > > What? I know nothing. > > --Eric > _______________________________________________ > drbd-user mailing list > drbd-user@lists.linbit.com > http://lists.linbit.com/mailman/listinfo/drbd-user >
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