Idea for a ‘2-in 1-out’ drive system

[adriencater]

I’d like to build a primary external storage drive based on a 3-disks-in-rotation principle, with 2 disks in a drive and a 3rd disk off-site.

 

The two disks in the drive would act like a RAID-1 drive. A third disk would be an off-site backup. I would rotate the disks between the drive and the off-site.

 

i.e.: In the morning, I would remove one of the disks from the drive, take it to work, take the third disk that was at work back home, put it in the drive, the ‘new’ third disk would be brought up to date with the disk already in the drive; repeat on a weekly basis

 

My thinking is that this would offer the advantages of RAID-1 insurance against random disk failure, while having an off-site backup which is only a few days old in case my house burns down (unlikely) or I do something stupid like erase an important directory (more likely than I’d like to think).

 

The system would have to be robust enough to not panic when a disk is randomly removed (even if I continue to work on the drive with only one disk in it), and smart enough to quickly copy/sync the newer data when a disk is inserted.

 

Any ideas?

 

 

(PS: first post, hello. A friend has a Lime box, and suggested I post this idea here...)

[WeeboTech]

There are multiple ways of syncing the spare drive.

The problem is you want to take a drive out, and bring another different drive home.

 

From what I understand, with only 2 drives, PARITY + Data #1, they are actually a mirror.

However I'm not sure Data #1 could actually be reconstructed. from only the parity disk.

(Worthy of a test).

 

 

 

 

I might be more inclined to do this with extra drives.

 

I would leaving parity and data #1 always present and intact.

 

With data #2 (and/or 3) being the drive moved back and forth, you could mount the drive, use rsync to bring them into sync and then remove it. 

 

You could also reconstruct data #1 into another slot (using data #2 or #3) and after reconstructed, remove data #1 for the backup.

 

Now your system is up to date using parity and one of the other drives.

 

[vca]

I’d like to build a primary external storage drive based on a 3-disks-in-rotation principle, with 2 disks in a drive and a 3rd disk off-site.

 

I do something similar, though not by breaking/rejoining a raid set.  I have a backup program (see http://arcvback.com/arcvback.html ) that creates a single full backup followed by a very large number of incremental backups and stores these to a pair of removable USB attached drives. So every few days I run the backup program and it searches my UNRAID box (which is mainly media files) for new or changed files, these get saved to a cache area on a local drive in another computer (where the backup program runs).  Then the cached data gets written to one of the external USB drives.  Now I have the original data plus two copies of it (one in the cache and the other on the USB drive). Periodically I take the current USB drive offsite and then swap it for the second USB drive.  When the second USB drive is brought back I run a flush of the cache which brings this drive up to date (so now both the local and offsite USB drives have a complete copy of the backup data) and frees up space on the cache drive for another cycle. In this way I have a RAID protected primary copy of all files plus two backup copies (either on the cache and one USB or on both USB drives) at almost all times.

 

This system is not limited by the size of a single external USB drive, so if you have more than will fit on a single drive you just continue flushing the cache to another drive.

 

Obviously the initial full backup takes a long time to run (this can be done in multiple passes if your cache space is limited), but after that the incremental backups run quite quickly (say in the range of 10 - 60 minutes depending on the amount of data that was added since the last backup pass).

 

Regards,

Stephen.

 

[RobJ]

Some additional ideas, sounds like you want a 3 drive RAID 1 with auto-syncing, so you might want to investigate solutions that could provide that.

* Perhaps lvm can do it for you?  Then you can use any standard Linux based system.

* Perhaps the 4 drives controlled by DriveExpert?  Look for a motherboard, such as some of the P45 Q's with DriveExpert.

* Check the various 4 drive RAID cards.

 

I have no personal experience with any of the above.