On Fri, 2013-07-05 at 13:10 +0200, David Brown wrote:

I apologise if this is preaching to the converted.  When you are
concerned about data resilience, RAID is only part of the answer - I
just want to make sure you have considered everything else.

Sure... I make regular complete backups, on different types of storage
media (magnetic vs. optical - yes I do fear very strong coronal mass
ejections ;-) )... being placed in different locations (even different
cities ;)

The main benefit of RAID is availability - you don't have downtime when
a disk fails.  It also ensures that you don't lose data that is created
between backup runs.  But it is not the solution for data safety and
reliability - that is what backups are for.

Sure...

You need to look at the complete picture here.  What are the risks to
your data?  Is a double disk failure /really/ the most likely failure
scenario?  Have you considered the likelihood and consequences of other
failure types?  In my experience, user error is a bigger risk to data
loss than a double disk failure - I have more often restored from backup
due to someone deleting the wrong files (or losing them due to slipping
when dragging-and-dropping) than from disk problems, even with non-raid
setups.

Hehe... I once accidentally mke2fs'ed (instead of fsck) over my main
personal data fs (and fucking e2fsprogs don't check for existing
fs/containers, AFAIK till today)... and back then my most recent backup
was really old... like 2 years or so...
I invested like 2 weeks of ext4 forensic and managed to basically
recover all of the data out of the overwritten fs... ;)

Raid will help if one of your disk dies, but it will not help against
fire or theft, or hardware failure on the NAS, or software failure, or
user error, or malware (if you have windows clients), or power failure,
or any one of a number of different scenarios.

So depending on your circumstances, you might get better "data
security/resilience" by putting the extra disks in a second machine at a
second location, or other mixed primary/secondary arrangements.

sure... see above... I do have a good backup strategy now :)

Anyway... for the daily growth of data... RAID does a good "backup-like"
job in helping me against disk failures... since I simlpy can't backup
everything every day...


Cheers,
Chris.