Hi list,
I would like to understand if this is a lvmthin metadata size bug of if
I am simply missing something.
These are my system specs:
- CentOS 7.3 64 bit with kernel 3.10.0-514.6.1.el7
- LVM version 2.02.166-1.el7_3.2
- two linux software RAID device, md127 (root) and md126 (storage)
MD array specs (the interesting one is md126)
Personalities : [raid10]
md126 : active raid10 sdd2[3] sda3[0] sdb2[1] sdc2[2]
557632000 blocks super 1.2 128K chunks 2 near-copies [4/4] [UUUU]
bitmap: 1/5 pages [4KB], 65536KB chunk
md127 : active raid10 sdc1[2] sda2[0] sdd1[3] sdb1[1]
67178496 blocks super 1.2 512K chunks 2 near-copies [4/4] [UUUU]
bitmap: 0/1 pages [0KB], 65536KB chunk
As you can see, /dev/md126 has a 128KB chunk size. I used this device to
host a physical volume and volume group on which I created a thinpool of
512GB. Then, I create a thin logical volume of the same size (512 GB)
and started to fill it. Somewhere near (but not at) the full capacity, I
saw the volume offline due to metadata exhaustion.
Let see how the logical volume was created and how it appear:
[root@blackhole ]# lvcreate --thin vg_kvm/thinpool -L 512G; lvs -a -o
+chunk_size
Using default stripesize 64.00 KiB.
Logical volume "thinpool" created.
LV VG Attr LSize Pool Origin Data%
Meta% Move Log Cpy%Sync Convert Chunk
[lvol0_pmspare] vg_kvm ewi------- 128.00m
0
thinpool vg_kvm twi-a-tz-- 512.00g 0.00 0.83
128.00k
[thinpool_tdata] vg_kvm Twi-ao---- 512.00g
0
[thinpool_tmeta] vg_kvm ewi-ao---- 128.00m
0
root vg_system -wi-ao---- 50.00g
0
swap vg_system -wi-ao---- 7.62g
0
The metadata volume is quite smaller (~2x) than I expected, and not big
enough to reach 100% data utilization. Indeed, thin_metadata_size show a
minimum metadata volume size of over 130 MB:
[root@blackhole ]# thin_metadata_size -b 128k -s 512g -m 1 -u m
thin_metadata_size - 130.04 mebibytes estimated metadata area size for
"--block-size=128kibibytes --pool-size=512gibibytes --max-thins=1"
Now, the interesting thing: by explicitly setting --chunksize=128, the
metadata volume is 2x bigger (and in line with my expectations):
[root@blackhole ]# lvcreate --thin vg_kvm/thinpool -L 512G
--chunksize=128; lvs -a -o +chunk_size
Using default stripesize 64.00 KiB.
Logical volume "thinpool" created.
LV VG Attr LSize Pool Origin Data%
Meta% Move Log Cpy%Sync Convert Chunk
[lvol0_pmspare] vg_kvm ewi------- 256.00m
0
thinpool vg_kvm twi-a-tz-- 512.00g 0.00 0.42
128.00k
[thinpool_tdata] vg_kvm Twi-ao---- 512.00g
0
[thinpool_tmeta] vg_kvm ewi-ao---- 256.00m
0
root vg_system -wi-ao---- 50.00g
0
swap vg_system -wi-ao---- 7.62g
0
Why I saw two very different metadata volume sizes? Chunksize was 128 KB
in both cases; the only difference is that I explicitly specified it on
the command line...
Thanks.
--
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti@assyoma.it - info@assyoma.it
GPG public key ID: FF5F32A8
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