CT storage backends

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Comparison tables

Solidity in front of failures and security

Feature OVZ Ploop OVZ SimFS (ext4) LVM (ext4) ZFS
I/O isolation Good Bad: Some bug could be exploited to escape CT and access HN file system [1] [2] Good Good
Reliability Low: big amount of files produce ext4 corruption so often Medium: fsck, power loss and HW Raid without cache can kill whole data High: LVM metadata can be corrupted completely Excellent: no write hole, checksumming and COW
Filesystem over filesystem Yes No No ?
Effect of HN filesystem corruption at /vz No effect Same FS ? ?
Maturity in O/VZ Since 2012 Since ~2005 Since 1998 Since 2014

Performance and design features

Feature OVZ Ploop OVZ SimFS (ext4) LVM (ext4) ZFS (~simfs)
Maximum container volume space 4 TiB [3] 1 EiB [4] ? 256 ZiB
Wasted space due to architecture up to 20% No up to 20% ?
Disk i/o speed Fast in any case Very fast with small amount of containers Fast in any case Fast in any case
Disk space overcommit (provide more space for containers than available on server now) Yes Yes No Yes
Different containers may use file systems of different types and properties Yes No Yes No
Second level quotes in Linux (inside container) Yes Yes Yes Not implemented
Potential support for QCOW2 and other image formats Yes No No No
Incremental backup support on filesystem level Yes, through snapshots No No Yes

Administrator operations

Feature OVZ Ploop OVZ SimFS (ext4) LVM (ext4) ZFS (~simfs)
vzctl integration Complete Complete No, many manual operations No, some manual operations
External compaction for container volumes Needed for saving HN space No Not available Not required
Access to private area from host Yes Yes ? ?
Live backup Easy, fast and consistent[5] [6] Easy, slow, and sometimes inconsistent in case some application depends on inode IDs Fast Fast theoretically
Snapshot support Yes[7] No theoretically, because of much/small files to be copied Yes Yes
Live migration Reliable and fast Not reliable and slow, if some application depends on inode IDs Not implemented Fast theoretically
Continue failed CT migration Yes, in vzctl from OpenVZ -stable Yes, option "--keep-dst" Not implemented ?