My own strategy is born out of unfortunate bloodletting. Back when I
used to do a lot of wedding photography with film, I went to a
two-camera strategy. EVERY critical shot is photographed with two
different cameras. This wasn't that big of a burden because there
really aren't that many critical shots, but if you happen to miss "The
Kiss", you're screwed. One wedding, I lost most of the "formals"
because three or four shots into a roll, the PC socket had loosened on
the inside of the camera and the flash was firing when the mirror went
up, instead of when the shutter was open. An unique failure that John
Hermanson managed to quickly diagnose and dispatch out of the camera.
But I had backed up most of the critical shots with one "safety shot"
in the IS3. It was a success except for ONE picture I didn't have. The
ONE picture the MOB wanted most, of course.
Another reason why I had gone to this method was film processing
failure, or lost package. Every roll of a wedding was numbered and
letter coded as to which camera and part of the day it was taken.
Everything was kept separate and only one set was processed on any
given day. No matter which camera I used for a given shot, if it was
important, I always did a safety shot on the other camera. Of course,
it was a compromised image because of lens selection or flash/noflash,
but at least I had something to work with.
With digital, I continue this model for professional shoots. I assume
a card failure, file corruption, and more likely photographer error
that causes an issue that isn't seen when chimping. There are a
multitude of failures that can occur which have nothing to do with the
storage medium itself. But I don't need to go crazy with tens of
cards. I just need two cards and two cameras. Statistical analysis
shows acceptable risk with this. In fact, statistically, the more
cards you use, the higher the likelihood of failure--but with
decreased amount of project risk. A two-engined jet is MUCH more
reliable than a single-engined jet, but if you are 180 minutes out
over the Pacific, you may want that second engine.
It has taken me years to talk about it, and I'm still rather loath to
go into details, but I lost part of 2007, all of 2008, and part of
2009 to a hard-drive storage system failure. My dual-drive NAS
corrupted and nearly everything on the drives was destroyed. I had
some images on my computer's hard drive for faster editing, etc., but
everything was backed up on CD-ROMS which were kept at the bank.
During the restoral process, I discovered that EVERY CD-ROM I had
burned for the year was damaged by a faulty writer. The only CDs that
could be restored were written before the drive went bad. And, yes, I
lost most of a wedding!
So, now I assume nothing. I have three sets of drives, plus I rent a
server/storage down in Texas where I upload everything.
However, about a year ago I went through the process of upgrading my
drives from 2Tb to 4/5Tb drives. In doing so, the file copy process
revealed a corrupted drive and through it all, I ended up losing two
months of images. However, when the dust cleared I was able to restore
two weeks worth of images that had been uploaded to the Texas server
(the rest had not been uploaded) back down to my portable drives.
As to memory cards going bad or corrupting, I would love to say that
this has never happened to me with a camera, but that's not entirely
true. I've had two failures that I can think of. I had a 1Gb CF card
get corrupted in the E-1 which ended up costing me the last 10 images.
And I had a 4Gb SD card lose die in the 6D with the loss of a few
images. However, in both cases, I knew I was having troubles and
didn't get surprised. I popped the card and battery out of the camera,
popped the battery back in and a different card and continued on my
way. The Canon was particularly sensitive to card corruption when the
power is interrupted or you pop the card out before everything stopped
writing. Every other camera I've used would corrupt the file being
written, where the Canon would corrupt the card. I'm certainly not the
only person who has encountered that either as various photography
forums have had this a topic of discussion for years.
Themed Olympus Photo Exhibition: http://www.tope.nl/