[Leica] about NAS devices

[reid at mejac.carlsbad.ca.us (Brian Reid)]

The term "NAS" stands for "Network Attached Storage". But NAS boxes are 
being used in other ways. Here's some background and explanation.

NAS boxes provide 3 core functions:

1. Aggregation. You can have a bunch of drives but talk to them as if 
they were just one drive. This way you don't have to remember which 
drive you put something on. A NAS is seen by your computer as just one 
drive, regardless of how many drives are actually in it.

2. Access. This is the "NA" part of NAS, and is why they were invented. 
If you have a NAS box and it is connected to an ethernet, then more than 
one computer can access it without you having to move any wires.

3. Safety. NAS boxes can (if you want) combine multiple drives in such a 
way that if one fails, you haven't lost any data, and theoretically you 
can replace that one failed drive and keep going. Doing this gives you 
less overall storage (you have to store multiple copies of data in order 
to make this work) but more reliability.

There are dozens of other non-core functions that add stress, 
complexity, and marketing advantage to a NAS box. You don't have to use 
any of them, but some are awfully convenient.

If two computers are trying to access the same storage, they need to 
take special care to make sure they don't trip over each other. If 
Computer A and Computer B are trying to update the same storage at the 
same time, it will make a mess. To prevent this from happening, software 
programmers use a technique called "file locking". Unfortunately, 
standard file locking techniques don't work with ethernet, so many 
applications (such as Lightroom) just say "sorry, you can't do that". 
Lightroom won't let you access a catalog across an ethernet because it 
doesn't want to be responsible for getting the locking done right.

If you use a NAS box but access it by a USB cable, then you are not 
using it via a network and therefore are not subject to network file 
locking problems. You get functions 1 and 3.

I use NAS boxes extensively, but I am a sufficiently jaded computer 
systems person that I will never trust them to do simultaneous shared 
access because of the inherent complexity of those file locking 
protocols.

But this is just me and my family. When I managed the IT department for 
a big company, I couldn't make "no sharing" rules, so instead I had to 
make and enforce rules for sharing.  I am long gone from the big 
companies whose IT departments I managed, but my rules remain pretty 
much as I wrote them, which is:

* Never edit on a NAS. Make a local copy and edit that, and put the 
edited copy back when you are done. Even though a NAS can be used as a 
virtual drive to edit in place, don't do it.

* Devise, use, and enforce a system to coordinate your updates with 
other people. I always use a "check-out/check-in" model. To edit a file, 
check it out of the library. When you are done editing and have uploaded 
the revised version, check it back in. The check-out process must 
prohibit the checking out of a file that someone else has checked out.

My personal process to manage my files (including photographs) is to 
keep the master copy of everything on a NAS at my house, to have that 
NAS automatically copied every night to storage that is not in my house, 
and to do check-out/check-in of files from the home NAS to my computers. 
The reason I use check-out/check-in even though it's just me doing it is 
that I have more than one computer. If I start an edit on my laptop, and 
then try to edit from my iMac, it will not let me do it.

Because I am paranoid and suspicious, I actually have 2 NAS devices from 
different manufacturers at my house, and replicate the master copy to 
the mirror copy by an automatic means. (Master is ReadyNAS, mirror is 
TrueNAS).

I also run Time Machine service on my master NAS device. Time Machine 
data is part of what is copied every night to offsite storage.