Hi,
in an environment of
- raid
- LVM on raid
- DRBD on LVM
- xen guest on DRBD
the space of the device needs to be cleaned (overwritten by zeroes or random)
before deletion of the logical volume.
The usual steps would be
# drbdadm down drbd6_2
# shred -n0 -zv /dev/vg1/lv_drbd6_2
# lvremove /dev/vg1/lv_drbd6_2
This works nice for small devices (up to 10 GB):
# time shred -n0 -zv /dev/vg1/lv_drbd6_1
shred: /dev/vg1/lv_drbd6_1: pass 1/1 (000000)...
shred: /dev/vg1/lv_drbd6_1: pass 1/1 (000000)...800MiB/10GiB 7%
shred: /dev/vg1/lv_drbd6_1: pass 1/1 (000000)...1.9GiB/10GiB 19%
shred: /dev/vg1/lv_drbd6_1: pass 1/1 (000000)...2.9GiB/10GiB 29%
shred: /dev/vg1/lv_drbd6_1: pass 1/1 (000000)...3.8GiB/10GiB 38%
shred: /dev/vg1/lv_drbd6_1: pass 1/1 (000000)...4.9GiB/10GiB 49%
shred: /dev/vg1/lv_drbd6_1: pass 1/1 (000000)...5.9GiB/10GiB 59%
shred: /dev/vg1/lv_drbd6_1: pass 1/1 (000000)...7.0GiB/10GiB 70%
shred: /dev/vg1/lv_drbd6_1: pass 1/1 (000000)...8.1GiB/10GiB 81%
shred: /dev/vg1/lv_drbd6_1: pass 1/1 (000000)...9.2GiB/10GiB 92%
shred: /dev/vg1/lv_drbd6_1: pass 1/1 (000000)...10GiB/10GiB 100%
real 0m48.919s
user 0m0.544s
sys 0m11.917s
But for larger ones e.g. 100 GB it blocks the IO on the XEN-node, triggering
alerts in the monitoring of other running XEN-guests.
As far as I googled ionice would not work.
What I found as solution is piping through pv:
# time dd if=/dev/zero | pv -L 100M | dd of=/dev/vg1/lv_drbd7_2
dd: writing to `/dev/vg1/lv_drbd7_2': No space left on device
]
2GB 0:01:32 [22.1MB/s] [ <=>
]
4194305+0 records in
4194304+0 records out
2147483648 bytes (2.1 GB) copied, 92.9986 s, 23.1 MB/s
real 1m33.005s
user 0m7.532s
sys 0m52.443s
Is there a better way?
TIA
Helmut Wollmersdorfer
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