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hardware vs. software raid5?

U

unhappy_mage

[H]ard|DCer of the Month - October 2005
Joined
Jun 29, 2004
Messages
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On /. yesterday there was a discussion regarding a way to store large amounts of data. Look here for further discussion of this. About 5 or 6 pages down, there is a mention of software raid being _faster_ than hardware raid. Has anyone got benchmarks on this?

I'm building a file server (any day now...), so I'd really be interested in getting 4 cheap-o sata controllers rather than one expensive one. If software raid5 is worthwhile, then I'd definitely take that route. Note that this machine will have duallie opterons (so no lack of cpu), 3 pci busses (so no lack of bandwidth) and will only be doing storage-type operations (so no other load). I know it's gonna be expensive either way, but saving $400 would be nice.
 
I would recommend a hardware RAID solution for RAID 5. Most RAID controllers that support RAID 5 have onboard RISC processors to perform the number crunching necessary to generate the parity data that allow RAID 5 to be feasible. A software based RAID 5 array might be faster, but that would be because your system's CPU would be performing those parity calculations. Your system's CPU is faster than the onboard processor on a hardware driven RAID controller, so that aspect of performance would be increased. However, this would eat up CPU clock cycles and slow your system's overall performance.
 
Software raid is also OS dependent, meaning your OS install takes a dive, and you could loose the raid, where as the hardware raid is dependent on the drives or the controller or the drives themselves (ie I can migrate my 4 disk raid 5 array from my 3ware 6410 controller to my new 7506-12 controller and the new controller will see the array already preconfigured).
 
you can import a software RAID5 array as well (Dynamic Disks) in NT\W2K\XPpro but not home
Id imagine the same would be true with a Linux array
so provided the drives are OK you can migrate to the same or even a different OS (among those listed)
but as mentioned a hardware RAID card with a dedicated XOR engine or processor is the way to go, substantially reducing the CPU impact

http://www.jsiinc.com/SUBN/tip6700/rh6714.htm
Moving Dynamic Disks
If you move dynamic disks between systems, you may not be able to move the dynamic disks back to the original host. Success depends on the number of dynamic disks that you move and the number of dynamic disks that the target system contains. Microsoft recommends that you do not move, and then import dynamic disks to another computer if the following conditions are true:
That destination computer contains a dynamic disk.
You may want to return the dynamic disks to the original computer in the future.
If you can, move all the dynamic disks from a computer at the same time and make sure that they are all available before you try to import them to the new host.
Click to expand...

more
 
I like the performance of my Netcell card but have to OC the pci bus to get best possible speed on this board. 3Ware Raid 5 cards definitely rock, I have to run 48MHz pci to approach that level of performance . Highest I can go on non-server based board. I'd really like to see this card on a 66Mhz pci. Clocking from 33 to 48MHz on PCI bus raised data throughput levels from 87-118MB/s. Accidently disconnected one of my HD's, took the card less than 2 hours to completely rebuild the array to full strength. I can only imagine the drain on a CPU, to rebuild a defective or missing HD in software Raid 5.

Oh yea, if the numbers sound pretty shabby, remember, no F6 needed during windows install or repair, detected as a single large ide drive by windows. Only running UDMA 5, gotta work on that. 5-200GB SATA drives on this bad boy would rock (especially if you have a spare 66MHz PCI slot.). HDTach graph is really weird looking, no drop off near end of drives. I uploaded the OC'd and not, runs with the card. 12 port 3Ware card would be better, I can't power it with one crappy 550 PSU.

Ice, how high a UDMA level can I reach? Really should just move the card and find out huh? I'd be better off without sound, and Lan on the PCI bus.

Will clocking the AGP Bus to 96 MHz kill the video card? Very clockable Vid card so I read, but usually done via software.
 
glad to hear the responses. leadman: overclocking your pci bus probably isn't the best idea. my $.02.

the point is, _if_ you don't care at all about cpu hit, then is software raid5 worth it? all this system is gonna do is take packets in on gigE and spit them back at the disk. dual opterons are probably overkill for this ( :cool: ) but i really need to go that high to get the 64-bit pci, and cool factor.
 
How many people will have simultaneous access? The RIG in Ice Czar's SIG sounds kinda like what you plan. My guess, and it is just a guess, is that biggest limitation may well be server OS planned, and compatibility with Hardware. One bonus to the HardCard solution, is that in the event of catastrophy, rebuild is handled outside OS. I was swapping pci cards around last night (stupid thing to do intoxicated), and knocked connector to 1 drive loose. Parity drive(doh), no normal reboot, no windows. Noticed on second attempt after entering Card bios, array degraded. Rebuilt via bios, windows all good again. Consider the benefit of bios level rebuild. Is the data worth the extra security?
 
Ice Czar said:
you can import a software RAID5 array as well (Dynamic Disks) in NT\W2K\XPpro but not home
Id imagine the same would be true with a Linux array
so provided the drives are OK you can migrate to the same or even a different OS (among those listed)
but as mentioned a hardware RAID card with a dedicated XOR engine or processor is the way to go, substantially reducing the CPU impact

http://www.jsiinc.com/SUBN/tip6700/rh6714.htm


more
Click to expand...

you cant import a RAID5 into any of the pro/home os's only server and above...
 
my software raid5 array most certinly ported from one of my xp pro systems to another
take note this was a scsi system and all the drives were on the same cable (6x18gb drives)
though both systems were SP2 so it might have been added in for SP2 RC2

mac systems are far cooler
you can make a raid5 array out of any set of 3+ drives.....
i have 8 32mb usb keys pluged into an 8 port USB hub on my
older (g4 500) powerbook using 10.3.3 i have them running in a raid 5 array
i have been told that using OSX you can make a raid5 array out of USB floppy drives
 
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