Methods Change Raid from 0 to 1+0 compare ?

[Abbas Parsafar]

We want to change raid configuration on important redhat linux servers with kernel 2.4 and 2.6 ( from raid 0 to 1+0 ).
We know that there are two methods to do this:
1) Online method : in which OS is up ( using hpacucli command )
2) Offline method : in which OS is down ( using raid configuration )
Could anybody compare these two methods for us ?
We want to understand all advantages and Disadvantages of these methods.

[Steven E. Protter]

Shalom,

If you used the OS and software raid, you will have to down the OS and re-install.

If you have a spare disk and hardware raid, you can use utilities built into the raid card to do the job.

To compare your methods, obviously if you can get away with doing it with the OS up, you go for that.

Before starting, take a full backup of everything.

SEP

[Matti_Kurkela]

Because you mention hpacucli, I assume you're talking about SmartArray hardware RAID - is this correct?

For the online method, you can also install & use a web-based Array Configuration Utility GUI (cpqacuxe package). But the choice of the tool is only a matter of personal preferences.

1) Online method

++ The system can provide normal service while the configuration change is happening.

-- Because the change from RAID 0 to 1+0 means essentially copying everything, there will be a lot of disk I/O, the system performance is going to be somewhat reduced while the operation is running, and the operation may take a longer time than using the offline method.

(Some SmartArray versions might allow you to adjust the background copy speed, so you can choose the level of performance reduction.)

2) Offline method
-- The system will be completely down until the configuration change is complete.

++ Because all the system's disk I/O capacity will be dedicated to the data copy operation, the offline method might be somewhat faster than the on-line method.

MK