1 Synopsis

snapraid [-c, --conf CONFIG] [-s, --start BLOCK]
    [-f, --force] [-v, --verbose] [-e, --exclude PATTERN]
    COMMAND

snapraid [-V, --version] [-h, --help]

2 Description

SnapRAID uses a disk of the array to store redundancy information, and it allows to recover from a complete disk failure.

SnapRAID is based on the snapshot concept like a backup program. You decide the time to make the "sync" of the redundancy information, and you are able to restore all the changes done at a disk of the array, until the "sync".

The main features of SnapRAID are:

• You can start using SnapRAID with already filled disks. You do not have to reformat or copy your data.
• The disks of the array can have different sizes. You have only to use the biggest one for the redundancy data.
• The data in the disks is not changed in any way. It doesn't even need write access at the data.
• If more than one disk fails, you lose the data only on the failed disks. All the data in the other disks is safe.
• It doesn't lock-in your data. You can stop using SnapRAID at any time.

3 Misfeatures

• You have different filesystems for each disk. Using a RAID you have only a big filesystem.
• It doesn't stripe data. With RAID you get a speed boost with striping.
• It doesn't support realtime recovery. With RAID you do not have to stop working when a disk fails.
• It's able to recover damages only from a single disk. With a Backup you are able to recover from a complete failure of the whole disk array.

4 Getting Started

This disk will be dedicated to this pourpuse only, and you should not store any other data on it.

You have to pick the biggest disk in the array, as the redundancy information may grow in size as the biggest data disk in the array.

Suppose now that you have mounted all your disks in the mount points:

/mnt/diskpar /mnt/disk1 /mnt/disk2 /mnt/disk3

you have to create the configuration file /etc/snapraid.conf with the following content:

parity /mnt/diskpar/parity content /mnt/diskpar/content disk d1 /mnt/disk1/ disk d2 /mnt/disk2/ disk d3 /mnt/disk3/

At this point you are ready to start the "sync" command to build the redundancy information.

snapraid sync

This process will take some hours at best the first time, depending on the size of the data already present in the data disks. If the disks are empty the process is immediate. You can stop it at any time pressing Ctrl+C, and at the next run it will start where interrupted.

When this command completes, your data is SAFE.

At this point you can start using your data as you like, and peridiocally update the redundancy information running the "sync" command.

To check the integrity of your data you can use the "check" command:

snapraid check

If will read all your data, to check if it's correct.

If an error is found, you can use the "fix" command to fix it.

snapraid fix

Note that the fix command will revert your data at the state of the last "sync" command executed. It works like a snapshot was taken in "sync".

5 Configuration

This configuration file is located in /etc/snapraid.conf and it should contains the following options:

parity FILE

Defines the file to use to store the redundancy information. It must be placed in a disk dedicated for this porpose with as much free space as the biggest disk in the array. This option can be used only one time.

content FILE

Defines the file to use to store the content of the redundancy organization. It must be placed in the same disk of the parity file, or in another location, but not in a disk of the array. This option can be used only one time.

disk NAME DIR

Defines the name and the mount point of the disks of the array. NAME is used to identify the disk, and it must be unique. DIR is the mount point of the disk in the filesystem. You can change the mount point as you like, as far you keep the NAME fixed. You should use one option for each disk of the array.

block_size SIZE_IN_KILOBYTES

Defines the basic block size in kilo bytes of the redundancy blocks. The default is 128 and it should work for most conditions. You should use this option only if you do not have enough memory to run SnapRAID. It requires to run TS*24/BS bytes, where TS is the total size in bytes of your disk array, and BS is the block size in bytes.

For example with 6 disk of 2 TB and a block size of 128 kB you have:

memory = (6 * 2 * 2^40) * 24 / (128 * 2^10) = 2.3 GB

An example of a typical configuration is:

parity /mnt/diskpar/parity content /mnt/diskpar/content disk d1 /mnt/disk1/ disk d2 /mnt/disk2/ disk d3 /mnt/disk3/ block_size 256

6 Commands

• Make a backup/snapshot -> "sync"
• Check for integrity -> "check"
• Restore the last backup/snapshot -> "fix".

7 Options

8 Copyright

9 See Also