Monday, December 22, 2008

RPO and RTO

As soon as you start to deal with backup strategies, you will come across two abbreviations you need to deal with: RTO and RPO.

Recovery Time Objective (RTO) simply means the time in minutes until a crashed system is up and running again. For example, if your backup server is able to restore your entire file server within 60 minutes, you have a RTO of 60.

However, this does not say anything about if the data you have restored were from one hour ago, yesterday or from last year. This is defined by the Recovery Point Objective (RPO).

A quick example: You save your file server every night at 20:00 (8pm). One day, all data on this server is lost at 11:00 (11am). You then do the restore and everything is up and running again at 13:00 (1pm).

In this example, you had an Recovery Time Objective (RTO) of 120 minutes (11:00 - 13:00). The Recovery Point Objective (RPO) was however 15 hours (20:00 - 11:00).

Dealing with these values can be quite challenging, but sometimes the biggest problem is not to confuse RTO with RPO.

I simply remember RTO as "Ready to gO" (after a crash) so RPO means how old the backup can be.

Friday, December 19, 2008

Fixing the local Live Mesh client

In case you are also playing with Live Mesh from Microsoft, you might end up that the synchronization between your local Live Mesh client and the server goes havoc.

In my case, I didn't had any folders in my mesh but my local client still showed several folders as being available inside the mesh. Trying to delete them from the "Live Mesh Folders" resulted in this nice error message:

Request to MOE failed with status code
404 Resource not found

If this happens to you, simply should down the Live Mesh client, then search the your computer where MOE.exe is located. On my Vista box, it was C:\Users\TeX HeX\AppData\Local\Microsoft\Live Mesh\GacBase\.

Inside that folder, you will find a folder called Store. Simply delete it and start the client again. Although it will have forgotten all settings, the "Zombie" folders are gone as well.

BTW: In case the client does not accept a folder inside the "Synchronize folder with this computer" (Error 400): Check if the folder is not on a removable medium (USB Stick, SD Card). Live mesh seems to accept hard drives only at this time.