Time Machine disc space

[AndrewRodney]

Originally Posted by John_G_Walter

The Drobo's sole purpose is to protect you against the possibility of a drive failure. It does not maintain two sets of data, in fact, the data on the drives is not readable outside of the Drobo.

Right. I just don't, as yet see what this brings to the party. I have a Raid 1 (mirrored) array which basically does the same. In fact, I think if one drive failed, I could use the 2nd drive to back up all the data. What appears somewhat cool about Drobo is that unlike my solution, if I need more storage, I have to go out and buy two matched drives, create a new Raid and copy. But the downside to Drobo (aside from cost) is the so called proprietary format and the damn USB 2.0 (I'm using SATA).

In the event of a failure of one of the drives, absolutely nothing happens with regards to your working environment. Drobo works in the background to redistribute the data amongst the remaining drives.

What happens if you've got 200 gigs of data that needs to be redistributed due to failure but only 100 gig's of free storage left?

In the case of my off the shelf Raid (from Sonnett), I've got two mirrored drives so capacity is fixed. One is a clone of the other.

I want to like the Drobo but so far, don't really get it. Not at its current price point and speed.

[John_G_Walter]

Originally Posted by AndrewRodney

What happens if you've got 200 gigs of data that needs to be redistributed due to failure but only 100 gig's of free storage left?

Take a look at the calculator on the Drobo website: Data Robotics, Inc. | Drobolator. As an example, my current configuration has four 500gb drives, and you will see that it provides me with an 'actual' available space of 1.4 tb. The balance is used for protection. If one of the drives fail, my actual space is reduced to 929 gb.

If the amount of actual data on the drive at the time of the failure was less than 929 gb, then after reconstruction, my data would again be protected against a second drive failure. If it was greater than 929, then my data would be at risk until I replaced the drive.

You can use the calculator to see how different drive combinations affect the actual data capacity that you have. Again in my case, as an example, if I were to replace one of my 500 drives with a 750, I actually would not gain any additional capacity, as it appears expansion needs to be done in pairs.

As for its usefulness, I guess it really depends on what you want to accomplish. I looked at RAID 1 as a solution, and decided that it just wasn't flexible enough and suffered from performance issues as well since everything had to be written twice, all of the time. RAID 1 seemed like a good solution for a systems/applications drive where data wasn't changed a lot, and the need to get back up & running quickly could be accomplished with a duplicate drive. However, I currently back up my systems/application drive to a seperate external drive via Time Machine.

I too, was concerned about the USB connection, and I agree that it is somewhat slow. However, it has only appeared so far, to be slow in database operations such as reading my Aperture or Lightroom data. And, I really haven't tested it on a different drive since my libraries have grown, so that could be a cause as well. I have not seen a noticible lack of speed during normal PhotoShop file writing to the Drobo vs. a SATA drive, but I am sure there is something.

Proprietary issues are a concern as well, but I figure that is long as I have my data backed up and archived in other areas, than I can deal with Drobo going out of business or some catastrophe such as that.

[Martin_Doudoroff]

For what it's worth, Super Duper 2.5 supposedly provides Leopard support. The upgrade is free.

[jeffcable]

I am late to the party but for what it's worth here is my 2 cents...

Time Machine is a really excellent way to recover to a point just before you trashed a file. It is only storing changes and it does not copy files or folders that remain unchanged. It also does not make a brand new date-stamped copy of everything, every hour, day, week or month. It only backs up one instance of the data file and where there are 50 timed backups, 49 of them will have a uniquely named hard link to the actual instance of the stored data. UNIX permits hard links to data files and Time Machine can, very cleverly, hard link to directories as well.

I have recently upgraded to Leopard for my G4 PowerBook and I have been using Time Machine for the Month of February. It has been recording all of my file changes within around 4GB. With its method of deleting older backups, I guess that 500GB will be more enough space for my 80GB laptop drive. Clearly some form of backup is better than no backup. It was once thought foolish to rely on ANY hard drive as your SOLE backup medium. It is useful to view all hard drives, whatever their configuration, as purely temporary storage space. They are not generally considered to be archival quality storage solutions.

All hard disks will fail and using the manufacturer's MTBF, as your guide to which drive to buy, notwithstanding the fact that the drive may be warranted for 3 years, does not help you if your hard drive storage has just carried off all of your valuable data. The more hard disks you use in your solution to make backup copies of your work, the more you are increasing your risk of drive failure. In absolute terms, two disks will double (instead of halving) your risk of seeing a hard drive failure.

Of course more disks equal more risk of failure, which is why industry standard RAID solutions are usually RAID 3, 5 or 6 so that work can carry on in the event of a drive failure. A newer development is MAID (Massive Array of Inactive Disks) and that may be a technology that is about to become more common. The idea is that only the controller disk is turning and that all other disks in the array are inactive and will only be 'spun up' by the controller, to access them for specific read and write tasks. It is thought that this technology would help to increase the reliability of the disk drives in such an array. Consider tape drives as a possible archival solution as capacities increase and tape drives get cheaper to buy. Another emerging technology is the Blu-ray optical disks in 50, 100 and 200GB sizes. As writing the disks becomes more cost-effective, they may prove to be optimal archival media.

For interest, the following link provides a starting point when assessing the value of optical media as part of your image data archiving strategy. I have taken to using Taiyo Yuden DVD's in the burner that was originally delivered as part of the PowerBook.

Jeff

Optical media longevity

[Martin_Doudoroff]

This exhaustive article may be the last word on Time Machine until Apple makes significant revisions. The article takes some effort to slog though, but it contains lots of answers for questions that have arisen in this discussion thread, and it does a superb job contextualizing Time Machine.

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