software raid performance hit

[xyz]

Hi, I'm new in her :roll:
since this forum has the 'storage' name, maybe this is the right place for me to ask about raid.
I have new supermicro server with dual p3 tualatin 1.13, 512MB ram and two 18 GB ultra 160 scsi.
since this server is intended to running as mail server, backup is important. so my plan is to run in raid1. my question is, how much cpu/performance hit if I run in software mode? the software is windows nt4, but will running w2k server is possible

thanks

ps: I got your forum from folding@home teamstats, good folding :mrgrn:

 

[CougTek]

I don't know about RAID 1, but soft RAID 0 is usually much faster than what most hardware RAID solutions can provide. I don't remember the CPU utilization %, but I think it was around 40% on average during transfers on a modern computer some 6 months ago.

I have unfortunately never tried soft RAID 1, but if it's like soft RAID 0, the tranfer rates will be higher than hardware RAID, mostly because the generic purpose processor in your machine if a heck faster than the dedicated but dinosaur-age-technology RISC processor on the RAID card. The price to pay is higher CPU utilization and I'm also not sure that you can boot from a soft RAID array under Win NT4 (maybe Win2K can, but again I don't think so).

Welcome BTW.

 

[P5-133XL]

As long as all drives are running in ultra DMA mode and the CPU is 500MHz+, the performance hit for software raid-1 tends not be signifigent. There is no noticeable performance improvement with Software raid-1. There is a slight CPU usage increase and the standard block size becomes 64K rather than 128K and that tends to slow down drive speed slightly.

In NT4, and W2k (XP ????: I haven't tried it) You can boot to to a software raid-1 partition. The OS just deals with the raid-1 mirror as a single read-only drive until the raid drivers are loaded. For safety sake, you might consider changing your boot.ini to point to the second drive in addition to the first so that upon drive failure, you can boot from either drive without physically switching the order of the drives.

 

[Clocker]

Hope this helps a little:

 

[xyz]

wow :excl: thanks for the quick response, I come to the right forum :wink:
as for the booting, I already try unplug either of the disk. all seems to boot perfectly, if not. I just switch the bay. it's in the front of the casing, so it's not a big problem. However for software raid I must break the raid first, then shutdown, insert the other disk. then rebuild the raid from beginning. what's the case with hardware raid? it is truly hot-plug, so you don't have to shutdown and rebuild it again from beginning.

about the cpu utilization, looking at the graph I think I can accept that, consider that my machine is powerful enough and have a good ultra160 scsi.

 

[P5-133XL]

SCSI HW raid is normally truely hot-plug with no booting involved. However, you still have to break the raid, replace the drive and rebuild (unless there is a hot spare)