Hi All,
On 28/08/2012 11:24 AM, Christopher M. Bailey wrote:
I'm currently getting our DR system fine tuned at work, and as part of this I would like some software to take images of some of our larger Linux servers (RHCE 5 & 6) similar to how programs like Shadow Protect does for Windoze based systems, in other words while the system is live. Some of these server have up to 6TB of data stored on them and as you could appreciate, downing the server to run something like Clonezilla would take far too long to be practical. I would also like to be able to schedule these snapshots, say once a week.
Unless I am mistaken, all Shadow Protect does is create snapshot of the filesystem at a point in time. No different to taking an LVM snapshot. If at that point in time there are processes still with open files and data in memory, then you have every risk of corruption and lack of a suitable backup.
Unlikely. Windows VSS is _very_ good. Firstly, it allows snapshot sets to be taken atomically across multiple volumes (think /var/db_data and /var/db_logs) ensuring true crash-consistent snapshots. If /var/db_data and /var/db_logs were on separate LVM volumes under Linux, all bets are off. Secondly, VSS is tightly integrated with the OS. Any decent database or other application will provide a VSS writer which tells the backup application exactly how to back up the data for the database. To give an example, for Windows 2003 and older, when a VSS snapshot is taken the registry files are dumped to a different location and instructions are provided to the backup application to back the files up from there as if they were really in C:\Windows\System32\config. For an MSSQL differential backup, the backup application is told exactly which file fragments (eg offset 1234 length 456) have changed since the full backup was taken, so that only those need to be backed up. For Exchange, log truncation etc is handled automatically. Even without fancy instructions required, the VSS snapshot process gives applications a chance to ensure application level consistency. Sorry to sound like a Microsoft shill, but I've contributed code to the Bacula project to do all the above stuff so I can appreciate the differences. James