CT storage backends
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Comparison table
| Feature | OVZ Ploop | OVZ SimFS (ext4) | LVM (ext4) | ZFS | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 1. Solidity in front of failures and security | ||||||||||
| I/O isolation | Good | Bad: Possibility of "no inodes" issues (when file system journal become a bottleneck). | Good | Good | ||||||
| Security | Good | Bad: Some bug could be exploited to escape CT and access HN file system [1] [2] | ||||||||
| 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 | Using zvol | ||||||
| Effect of HN filesystem corruption at /vz | No corruption | Possible corruption | ? | ? | ||||||
| Maturity in O/VZ | Since 2012 | Since ~2005 | Since 1998 | Since 2014 | ||||||
| 2. Performance and design features | ||||||||||
| Maximum container volume space | 4 TiB [3] | 1 EiB [4] | ? | 256 ZiB | ||||||
| Disk space overhead | Up to 20% | No | Up to 20% | No, but if using zvol is up to 50% depending on volblocksize | ||||||
| Disk I/O speed | Fast | Fast only with small amount of containers per node, slowdown in case of big number of small files. | Fast | Fast | ||||||
| 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 | Using zvol | ||||||
| Second level quotes in Linux (inside container) | Yes | Yes | Yes | Using zvol | ||||||
| Potential support for QCOW2 and other image formats | Yes | No | No | No | ||||||
| Incremental backup support on filesystem level | Yes, through snapshots | No | No | Yes | ||||||
| Shared storage support (Virtuozzo storage, NFS) | Yes | No | Yes | NFS only | ||||||
| 3. Maintenance | ||||||||||
| 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 | ? | Only using ZFS filesystem | ||||||
| Live backup | Easy, fast and consistent[5] [6] | Easy, slow, and sometimes inconsistent in case some application depends on inode IDs | No | Fast via ZFS Send/Receive | ||||||
| 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 via ZFS Send/Receive | ||||||
| Continue failed CT migration | Yes, in vzctl from OpenVZ -stable | Yes, option "--keep-dst" | Not implemented | ? | ||||||
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