[Info-vax] ODS-5 data/file recovery

[David Froble]

Stephen Hoffman wrote:
> On 2013-02-17 01:28:00 +0000, David Froble said:
> 
>> MG wrote:
>>
>>> Do you have terabytes to back up?  Because that would be one of the
>>> issues I'd have to overcome.
>>
>> No, and that makes it much easier.  Most of my disks are rather old, 1 
>> GB, 2 GB and such, and not very full.  I've also got some 36 GB disks 
>> on my Alpha, and I use these strictly for image save sets of the 
>> smaller disks.
>>
>> Frankly, while it's a bit more complex, backing up just what has 
>> changed works rather well.  With terabytes of storage, I've got to 
>> believe that 99% of it does NOT change on a daily basis.  So it still 
>> should be a managable thing.
> 
> Storage prices are headed back downward, again.  Four-terabyte 6 Gbps 
> SATA disks are US$210 on Amazon.
> 
> With smaller SCSI storage configurations, I've rolled out new 146 GB 
> SCSI drives into some older configurations; those were US$40 each, when 
> reusing some "spare" parts.
> 
> When it comes to making data backups, it's a case of capturing the data 
> churn while avoiding copying out data that's easily recoverable from 
> distro, as David states.  BACKUP does this incremental stuff fairly 
> well, though (as I've groused before) everybody gets to roll their own 
> DCL procedures.

If I don't know what's going on, I have a basic mistrust of "black box" 
procedures.  Yeah, I'm prejudiced.  I haven't reviewed the code in 
BACKUP, but I have this difference in trust between things on VMS and, 
for instance, weendoze ....

In any case, all backup procedures should be checked by doing a restore 
and making sure that what you thought you had saved is indeed 
recoverable.  When you actually need your backup is a poor time to find 
out if you actually do have a valid copy of your data ....

> So find your static data.  Add some disks for target storage.  Roll your 
> own DCL incremental BACKUPs.
> 
> I'm not so sure tapes make all that much sense for small shops and 
> hobbyists, either.  Yeah, tapes do work.  Decent choices for long-term 
> and off-site, too.  Tape drives (with decent capacity), libraries 
> (again, with decent capacities), and tape media are (fairly) expensive, 
> and (without a library or loader) require some manual effort.  For 
> transient and local backups and particularly hobbyist stuff, disks are a 
> cheap^Winexpensive choice.
> 

Back in "the day", tapes were the only decent method of storing a copy 
of your data.  I don't believe that tapes are a reasonable method to 
store data today.

My philosophy is basically to have a minimum of 2 copies of any data. 
Today's disks are rather reliable, and to lose 1 is rare, to lose both 
at the same time is, well, it sucks to be you.

As Steve mentioned, disks are smaller and cheaper than ever.  While RP03 
disk packs were removable, they were sort of, ummmm, LARGE.  You can 
have removable disks for multiple site storage to overcome local 
disasters.  Still, there can be events that can still cause you to lose 
data.  "Too bad about that comet!"

I don't know of anything better than today's magnetic disks for reliable 
storage of data.  Yes, they can fail.  They can develop bad blocks.  Two 
failing at the same time just doesn't happen.  Of course, you need to 
check on them periodically to see if one has failed.

Writable and re-writable optical disks can and will lose data over time. 
  That time can be rather short if you leave them sitting in direct 
sunlight ....