I have a few questions about RAID 5, BBWC (Battery Backed Write Cache), filesystem (ext3) and optionally mysql.
I have a hypothesis and I ask Server Fault community to validate or not this one:
- The system is UP, applications works with database and use transactions
- The RAID system is configured with RAID5, write caching and battery (BBWC)
With this solution, when OS receive write ACK, data are possibly in the RAID controller cache, and not in a persistent memory (my RAID drives disk).
If a power failure appears and data are in the RAID controller cache, the BBWC maintains data with the battery pack. Until then, everything is good.
But battery has a certain capacity, and it’s not infinite. If the power failure is longer than two or three days, the RAID cache is lost.
For me it’s a dramatic and likely scenario.
My questions are:
- Can ext3 solve this problem? Probably not
- Is it possible to corrupt mysql database?
- Mysql transactions are lost? I think so
Hardware: HP DL380 G7
OS: Centos 5 with ext3