[CentOS] Harware vs Kernel RAID (was Re: External SATA enclosures: SiI3124 and CentOS 5?)

Chan Chung Hang Christopher christopher.chan at bradbury.edu.hk
Wed Jun 3 15:25:54 UTC 2009

>> See my reply to nate. If you are using boards with 12GB of cache,
>> software raid is not even on the radar.
> True, but I feel an important point is being missed here.
> In order to avoid a lot of the random I/O file systems use page cache  
> to combine I/O operations and transaction logs to log it sequentially  
> before committing it in the background later but the ability of the  
> disks to handle a large amount of random I/O is also a big factor as  
> if the commits can't execute fast enough the log will not empty enough  
> to make it perform, so then you need an ever bigger log.

/me shrugs. It is not as if a hardware raid card is the only solution. 
One can try external journaling devices for the filesystem like a 
Gigabyte I-RAM drive or a UMEM card and still use md devices. Although I 
would not bother with a software raid setup if I had lots of disk arrays 
I suspect.

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