[Info-vax] OT: server farm backups

[mcleanjoh at gmail.com]

They probably take a SAN snapshot then save the data onto other disks.  If I understand it correctly, a SAN snapshot is quite clever.  It basically sets a check time, with disk blocks written to file after that time being written to a new area rather than overwrite the old blocks.  This means there is no "down time" while the disk is unavailable. 

Somewhere the SAN keeps a map (and presumably other identifying info) and after the new data is written that map is updated so that any read or write will access the new area rather than the old.

What you do with the snapshot is up to you.  You could write to tape, burn to CD or DVD, or write to another disk.  Archiving that snapshot can take place while the system continues as normal.