#6: Network based RAID-1

You are probably familiar with RAID-1, which is a mirroring technique for synchronizing data between two or more disks for the sake of redundancy. Normally, RAID-1 mirrors data between several local disks, but you can also sync them over Ethernet. This is not conventional RAID-1 but at least comparable.

To replicate data over network, there are two basic approaches. The first is to use a replicating FUSE (file system in userspace) on top of a network file system (or protocol, respectively). For instance, you can use Chiron FS to replicate between a local and a mounted NFS or SSHFS/SFTP drive. It's completely up to you which underlying file systems or protocols you use. The only requirement is that those have to be mounted. Of course, you can also set up two machines with hardware or software RAID-1 and LVM and then connect both with Chiron FS. There's no limit because Chiron FS runs at file system level, not at device level.

The other way is to use a native network based replication storage system such as DRBD. Unlike Chiron FS, this doesn't act upon file systems but beneath them. Such a storage system is comparable to an LVM with the major difference that it doesn't expand storage space but mirrors data. So in general, the difference between (network based) LVMs and DRBD is the difference between RAID-0 and RAID-1. Due to this architecture, DRBD isn't a file system, so you can use any file system you like on top of DRBD. In most cases, DRBD is used to build server clusters. There you have several server machines synchronizing their disks with DRBD. If one machine fails, another one can replace it immediately. If those servers just shared one single data source, all would fail if this source went down. Also the reading performance is much better compared to a shared data source because all machines act on their local hard drives.

The advantage of DRBD over Chiron FS is obvious: because the underlying mirroring architecture is completely transparent, you can make use of all features your chosen file system provides. Unlike Chiron FS, DRBD mirrors the complete block device as is. But on the other hand Chiron FS has the advantage that you can easily mount any drives on demand without having to build a fixed base architecture. So DRBD doesn't outclass Chiron FS because both satisfy different needs.

Read more about network based RAID-1:

• Linux.com: Chiron FS lets you set up RAID-1 over the network
• Chiron FS project website
• DRBD project website