HP/Compaq RAID Recovery – Delay Your Parity.
In the past week CDR – Manchester Data Recovery Services has received two HP/Compaq servers in for recovery. These servers / RAID controllers use a non-standard scheme of striping called delayed parity. Consequently they represent more of a challenge in the recovery environment than other servers. For those system administrators who understand the principles of RAID 5 parity and think they apply to HP/Compaq RAID, then unfortunately the rule book goes out of the window. We advise that if your data is important that you make no attempt at rebuilding the array or reinitialising disks – it could very well lead to data loss.
So, what’s different about the HP/Compaq RAID parameters? Essentially two different block sizes are used. One refers to the parity size and the other for the data. The parity block size is an integral multiple of data block size. In addition to this there are two further parameters that are required for a HP/Compaq RAID configuration – delay and firstdelay. Delay parameter indicates multiplicity, namely how many data blocks fit into one parity block; firstdelay shows how many data blocks are contained in the first parity block.
As you might guess by now, more than just guess work is required to find the correct configuration on a set of hard disks from a HP/Compaq RAID array. If drives are missing, not in their original order, or a bad rebuild has taken place, you require expert knowledge to make a full recovery of the data. If you do find yourself in this situation please contact us. Cheadle DATA Recovery Ltd has a free call out service to examine failed RAID arrays and servers.