RAID vs stuff on a HD

diglloyd · #15 02-14-2006, 10:27 AM

I have never experienced the need to defragment a large drive used for storing images . The OS is very smart about laying down files as contiguous blocks. Fragmentation is caused by deleting files regularly from existing ones, which opens up holes that later get filled. With large images, these holes are big enough that speed is very unlikely to be a problem.

However, I also try never to use more than 70% capacity of my drives. Not only are the outer tracks of a drive (or RAID set) about 1/2 the speed of the inner ones, as you approach being full, any potential fragmentation issues will begin to develop.

FYI, mirroring IMO is a bit dangerous. I've lost as many files due to "pilot error" as anything else eg deleting a file by accident. A mirrored drive just replicates that error to your mirror drive!

John_Luke · #16 02-14-2006, 10:39 AM

Lloyd-

I have heard this from others as well. I will heed your advice. People have told me that unless you are extremely anal about your file and drive practices and maintanance, RAID can be a dicey proposition.

I also swear never to mention deFrag again. ;-)

What about using a back-up utility like Retrospect? Do these types of products look for corruptions in each file and halt the process in in its tracks before moving that damage and ruining your back-up drive? I have heard the name DejaVue mentioned also. Seems like there are tons of back-up utilites out there. My head is swimming.

John_Luke · #17 02-14-2006, 10:55 AM

Before an entire HD is backed up, does anyone use the OSX Disk Utility to Verify/Repair that particular volume before it gets backed up? I guess RAID1 is out now, and I'm going to regularily back up to another drive. I just don't have back-up software picked out yet.

This makes it easier to kep that back-up drive physically protected and off site, like in a safe deposit box of safe.

diglloyd · #18 02-14-2006, 10:13 PM

[ QUOTE ]
Lloyd-

I have heard this from others as well. I will heed your advice. People have told me that unless you are extremely anal about your file and drive practices and maintanance, RAID can be a dicey proposition.

I also swear never to mention deFrag again. ;-)

What about using a back-up utility like Retrospect? Do these types of products look for corruptions in each file and halt the process in in its tracks before moving that damage and ruining your back-up drive? I have heard the name DejaVue mentioned also. Seems like there are tons of back-up utilites out there. My head is swimming.

[/ QUOTE ]

I use plain Finder copy coupled with a program I wrote that maintains cryptographic hashes on each file. Post-copy (backup), those hashes can be verified on the destination disk; even a single-bit variance will be detected with extremely high probability. I'll be releasing this program at some point.

If you are comfortable with command lines, you can use the 'diff' command to verify that source and backup are identical.

I don't use Retrospect, but it seems likely that it would offer a verify mode.