Message: 1 Date: Sun, 28 Apr 2013 20:04:01 -0700 From: "Millers' Photography L.L.C." <digitalimaging@dnmillerphoto.com>

I have never understood the phrase 'checksums'. I know for you all, it's important.

A checksum is essentially a hash. It's a mathematical algorithm that generates a unique result based on the contents of the file being checksummed. You can use that checksum as a tool to determine whether there has been any change to a file as even the smallest alteration in data of a checksummed file will generate a different unique result. So if the checksum originally calculated for a file is the same as one that later verified, you have a very high degree of certainty that the two files are identical. Of course, this requires that you checksum the original file in anticipation of verifying that the file is unchanged at a future time. As Chris indicated, checksums are now part of DNG. He was suggesting as one possibility that your data may still be intact or at least useful to you and a checksum mismatch could be interfering with you're ability to open your image. I personally do not know how to go about determining if that's what's happening.

From all your support, I have given up MIRROR RAID. And, of course I have to no way to use ECC in my two MBP Pro 8,3's.

Just one of these MBPro's could, maybe, have bought me a Mac Pro. Don't really know. Oh well. I like the idea of taking the imaging work with me. Yes….I could have could have and could have…

Now, I am manually using SuperDuper. I have dedicated two WD MyBook 1TB HD's for image file libraries. Another WD MyBook 1 TB HD is used with SuperDuper to clone the active internal HD. Time Machine is also active.

Don't want to make backup of backups. Have not yet figured out what chain of events I want to use to keep image files secure, archived. Having one main HD with image files, and not rotating, but keep cloning that one HD. Does that read good?

There are two concerns: 1) your backups could become corrupted or damaged; 2) file corruption could occur on the drive you're creating a backup from and in the act of creating a new backup, you're just copying the corrupted file. The easiest way to prevent something like that from happening is to have iterations of backups -- essentially a bunch of backups from different points in time so that if you discover a corrupted file, you haven't already replaced the one good copy of the file you had in a backup when you go to backup things again. Time machine is an example of an iterative backup system. Time machine has it's own problems but conceptually is a good start. It even allows for automatically rotating drives so you automatically have a backup of a backup. It's not always the greatest backup method for photographers though as its methods for determining whether a file has changed can fail, resulting in unnecessary file duplication. Further, it's slow and can't be used as a live backup like a clone can. If you are on a timetable with a client, nothing quite brings on the stress like searching trying to restore things from a time machine backup. For protecting their backups, some people employ multiple hard drives, tape drives, etc. so they can keep one drive offsite to ensure the safety of your backup from fire or theft. This is not my area of expertise, so I will refrain from offering advice. This is what I personally do (I have a MacBook Pro 8,2 and an iMac ... the particular model number evades me): I've replaced all my internal drives with OWC SSDs (primarily for the speed benefit but also because, for the most part, they're reliable and failure can be anticipated). If I'm on the road, the SSD and memory cards are my backup. When I get home, I copy the files to a Promise Pegasus (it's a RAID-5 enclosure with a thunderbolt connection) but work from the SSD. All the images I choose to retain that arent being worked on are removed from the SSD and spend their days on the Pegasus. Then I have a seagate backup plus thunderbolt adapter and three 4 TB drives that use with time machine to backup everything on the SSDs on the laptop and iMac and the photos I keep on the Pegasus. One of the three time machine drives I keep at my parents' house in a fireproof safe and I typically rotate the drives every two weeks. I do not clone my drives although, it's more because I'm lazy than because it's not important. I've replaced the internal optical drive in the MBP with another SSD that has a fresh system on it in case the primary SSD has a failure and I need to work immediately. The iMac has another SSD in it as well (got to love OWC). In the past, I've experimented with software based RAIDs and always had issues with them, so now I try and stick with a hardware controller like the one in the pegasus. If those exceed your budget, possibly look into drobo.

I had been using the image files right from the MIRRORED RAID, manipulate and save in the same spot on the RAID. Sometimes I bring the image files onto the internal HD for manipulation. Once ready for client, or printing, I think I will send the file back to the RAID. Think I will do the same with the pair of cloned HD's. Of course, I am expecting suggestions from the group. I can use those suggestions.

Keep in mind, a mirrored raid is not intended to ensure data integrity. It's purpose is to have a live clone of your drive that you can seamlessly move to if you experience a hardware failure. I suppose you could periodically rotate the secondary drive in the RAID (I'm not sure apple's implementation supports this; soft raid, if they're still in business, does).

Bringing me to another topic, FW400, or USB 2.0. No FW800 in this topic. Why? I only have one FW800 enclosure. All other external enclosures are USB 2 AND FW400. Not about to go out and purchase FW800 enclosures. The time cloning is not bothering me.

I have been looking at essays regarding which clones faster. USB 2 or FW400. I know I said clone, I really mean replicate image files that are plus or minus 200 mb's. SuperDuper tells me when using FW400 effective copy speed is about 5 mb's. With USB, effective copy speed ranges between 11 and 18 mb's. That's unusual. I typically find fw400 to be faster than usb 2.0. If it says it's faster using USB 2, go with what's faster.

I really have no idea what this all means. Clue me in, please.

Chris asks me how do I know the image files are corrupt. Photoshop CS5 gives me a message. Same with LR4. Once in a while I can view an image in preview. But not anywhere else. Maybe Chris has a suggestion as to how to determine what the underlying process is. I could guess that you might be able to open console and see if Photoshop or Lightroom are giving you error messages. Incidentally, if you see I/O error anywhere, that's a sign that your drives are failing and that's why you can't open your images.

Good luck! Morgan