Dne 25.10.2014 v 19:38 IB Development Team napsal(a):
W dniu 2014-10-25 o 14:50, Zdenek Kabelac pisze:
Is there any way to make LVM2 tools wipe added/freed LV space or plans to add
such functionality?
lvm.conf devices { issue_discard = 1 }
See it that fits your need ?
Note: when using this option - vg/lvremove becomes 'irreversible'operation.
issue_discard seems to require "underlying storage support" which is probably
not available in common RAID/SATA/SAS/DRBD scenarios. Universal, open (source)
solution would be better here probably (with hardware alternatives where
possible).
Yes - this discard needs to be implemented by underlaying storage.
When LVM based storage is used for guest virtual disks, it is possible that
after resizing/snapshoting LV, disk data fragments from one guest will be
visible to other guest, which may cause serious security problems if not wiped
somehow[...]
thin provisioning with zeroing enabled for thin-pool -Zy is likely better
option.
Sounds interesting. Is it stable solution for production systems? Does it
perform not worse than "regular" preallocated LV?
Provisioning does not come for 'free' - so you pay some price when you zero
provisioned blocks obviously - but blocks are zeroed on demand when they are
going to be used.
For production system - do not over provision space - if you promise too much
space and you don't have it - it currently require certain manual admin skills
to proceed with overfilled pool volumes - it's not yet fully automated.
Note: you could obviously implement 'workaround' something like:
lvcreate -l100%FREE -n trim_me vg
blkdiscard /dev/vg/trim_me
(or if disk doesn't support TRIM - dd if=/dev/zero of=/dev/vg/trim_me....)
lvremove vg/trim_me
If I understand correctly, in this scenario, guest data may still be present
outside "cleaned" LV (i.e. data that was saved outside LV in snapshot LV
during backups). If so - cleaning should be probably done transparently by LVM
"software" layer, even without "underlying storage support".
There is no such support on lvm2 side - it's much easier to be implemented
on the user side.
Before you call 'lvremove' - just dd zero volume - if lvm would be zeroing
devices i.e. 1TB volume on lvremove - that would be timely insane operation.
Regards
Zdenek
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