On Mon, 2007-03-05 at 20:24 +0100, Herbert Poetzl wrote: > On Mon, Mar 05, 2007 at 07:43:51AM -0500, Chuck wrote: > > On Monday 05 March 2007 06:15, Herbert Poetzl wrote: <snip> > > > > controllers. i would rather see the boss change the case to a 2u and > > put a real hardware raid controller in on a 2 card riser but...... it > > is not my call.. (and of course we find all this out after the machine > > has been in our production environment for 5 months) > > in most cases the hardware raid controller is not worth > the money, as a software raid usually gives a much better > performance with less latency and more control for the > operating system ... > > nevertheless, hw-raid can have some advantages if it is > done properly, e.g. auto reconstruction without affecting > the system performance and/or battery buffering in power > failure cases ...
I used to like the idea of hardware RAID but two things put me off: 1. When you pull the power on a system apparently the memory goes first but I/O systems function for just a bit longer - often writing junk data. This is apparently one of the things the high end UNIX vendors used to spend money on trying to get right. In short, you *need* a battery backed hardware RAID if you are serious about avoiding data corruption. These are more expensive. It also makes any form of RAID device that requires drivers to run (i.e. the soft-RAID devices on many modern machines) a little questionable to my mind. 2. Data corruption is serious because none of the formats the hardware RAID systems use are public. I am under the impression that in many cases even data recovery specialists do not have access to these. Thus you are completely at the mercy of the tools the vendor gives you. If they are buggy or you get into a situation (see above) that they can't recover from it's game over. Thus, I would *strongly* advise that unless you /need/ the performance a hardware RAID controller gives (and can then afford the UPS and the high level service contract with the vendor, etc.), use the Linux software RAID. If it all goes wrong you can always read the source and piece things together manually. I've had to do this. It's not fun but it is possible. For me it made the difference between having to tell my boss that the fileserver would be down for a while and having to tell my boss that we would have to revert to last months backup. HTH Cheers, - Martin _______________________________________________ Vserver mailing list Vserver@list.linux-vserver.org http://list.linux-vserver.org/mailman/listinfo/vserver
