Topic: Choosing between HW RAID (5) and kernel RAID

[paulmancan2]

One thing I like about kernel RAID is the elimination of the card as a single point of failure. I am however getting conflicting comments on performance; many suggesting that kernel RAID can be just as fast if not faster. So I am looking for more comments.

Here is my exact scenacrio:

I have to rebuild a server with a current OS (instead of RH 7.3 LOL.) It is currently a 1Ghz PIII w/2GB and an Adaptec 2100S with 3 X 18GB SCSI @ RAID 5. I have a 2nd matched CPU to add. I am trying to decide if I should keep the RAID (and maybe get a spare) OR go to kernel RAID. The server is primarly running a database.

Perhaps I should get a current benchmark. Is bonnie++ still the prefered method and if so if anyone has a good parameter specification for me to use that would be great... tried a few things with vastly differing results

Finally... why does everyone slam cheapo SW RAID cards... if these unload the work onto the host CPU how is this worse than kernel RAID?


Thanks!

[CharlieBrady]

Finally... why does everyone slam cheapo SW RAID cards... if these unload the work onto the host CPU how is this worse than kernel RAID?

Three issues that I'm aware of:

- performance - throughput and reliability may be worse than kernel RAID. With kernel RAID we know that there is ongoing development, and that the developers care a lot about reliability and performance. We don't have similar assurances for the various proprietary RAID cards.

- portability - SW RAID cards probably use proprietary layouts on disk. With kernel RAID, we know that we can take the disk(s) and boot them on any other linux system. With SW RAID cards, you may be tied to the hardware which you started with. If the hardware dies, you may be left with unbootable disks.

- downtime - with a SW RAID card, after a disk replacement you may not be able to reboot until after the RAID array is fully rebuilt.