software raid

[desktopsilver]

what is it ,,,,can i do it with an adaptec 29160 card ,,and windows 2000,,,,,,,any advantages /disadvantages

 

[cmdrdredd]

all RAID is in software...the software just formats the driver correctly. the controller is used to control the HD's input and output. You canot have pure hardware RAID there has to be some software to format the hardware.

 

[TNTrulez]

mmmm hardware RAID 5. That's the best config.

 

[cmdrdredd]

maybe I didn't explain that the best...point i was tying to make was...all RAID has software to controll it...nothing is pure hardware

 

[zoom8112]

all raid is done with software???

what about high end ide and scsi raid cards with onboard processors such as the intel i960

some controllers even have ram slots on them...

 

[cmdrdredd]

but buy that card and try plugging the HD in and go? guess what...Windows won't let you install anything on it gotta load the software to format for RAID 5 or whatever

 

[Windogg]

Not quite cmdrdredd

The term software RAID refers to using you CPU as the horsepower behind the calculations. Hardware RAID uses a hadrware device to handle the gruntwork. Thus with hardware RAID, CPU and resource utilizations is cut significantly.

Take ATA RAID for example. All of you Promise/Highpoint/IWill RAID adapters are really just an interface to connect you drives. Then it is left up to your CPU to do the work. Do any sort of data transfer and notice your CPU utilization spike up dramatically. Higher end ATA RAID Adapters like the Adaptecs and 3Wares have on board processors to crunch the numbers and DRAM to cache data. Check the CPU utilization and notice it stays nice and flat.

desktopsilver is thinking of using the built in software RAID in Windows 2000. IMHO it is an awful idea and an absolute waste of resources. First off you need to use MS dynamic disk. Not real benefit there except a major pain in compatibility in mixed mode environments. Next you will take a massive hit on CPU utilization as calculations need to be done on the data. The only time Windows software RAID might be considered is for mirroring (RAID1). If you are considering it for striping (RAID0), forget it. You can only do it on a non-boot paritition. That means you will be unable to use the equivilant space on your other drive(s) in RAID0.

Example: You have 2 x 18GB drives. Your boot parition is 4GB and a 14GB parition for your data. The largest RAID0 array you can have is 28GB (2 x 14GB). The other 4 gigs can still be used, just not in the array.

Same hold true for Windows software RAID5

By using software RAID with SCSI drives, you are really throwing out one of the major benefits of SCSI and that is low CPU utilization.

Windogg

 

[cmdrdredd]

yes but you still need some software to make the card do it's job and also to format the drives.

 

[Windogg]

Originally posted by: cmdrdredd
but buy that card and try plugging the HD in and go? guess what...Windows won't let you install anything on it gotta load the software to format for RAID 5 or whatever

Again, not quite. Yes some sort of driver will be needed for the OS to recognize the adapter. It is no different than anything else in the computer whether is a RAID adapter, hard drive controller, video hard, NIC, whatever. Take a SB Audigy and fire up a Windows 95 install. Does it detect it? Nope. Gotta install a driver.

 

[Budman]

Originally posted by: cmdrdredd
yes but you still need some software to make the card do it's job and also to format the drives.

If I were to go by your reasoning then everything needs software to run,you motherboard bios is software & you need it to run your system.

 

[Windogg]

Originally posted by: cmdrdredd
yes but you still need some software to make the card do it's job and also to format the drives.

cmdrdredd, you are misunderstanding software vs. hardware RAID and how each one impacts a system. We have the following:

Pure software Example: Windows RAID
Uses the OS and OS based software to handle all the work.

Hybrid Software/Hardware: Promise FastTrak, IWill SideRAID, etc.
Has a hardware interface for the drives but uses a combination of onboard logic and software to handle RAID functions. While it looks like a piece of hardware, it does not do any of the calculations.

Pure Hardware: Adaptec 2400A, 3Ware Escalade, Mylex, MegaRAID.
All logic is onboard a self contained controller. As many people have said these devices usually have their own CPU (i960 is a good example), memory for cache, and even battery backups to ensure all data in cache is flushed in the event of a power failure. Like any device it has a software driver to interface with the OS

 

[SCSIRAID]

To add to Windogg's correct explanation... A simple question can be asked to distinguish HW RAID from SW RAID. That question is 'where is the actual RAID application executed'. The RAID application is the code which does the mirroring and striping, distributes the reads among the data sources, regenerates the data from the defunct drive (RAID 5 critical array), rebuilds the defunct drive onto a new drive, scrubs the arrays looking for grown defects, etc etc. In card products like ATTO, Promise, Highpoint etc the answer is that the driver that gets loaded and executed on the host x86 CPU is where the 'smarts' are. The card is nothing more than a standard SCSI or IDE host bus adapter with its PCI Device ID modified so the OS will not recognize it and will ask you to provide the CD with the driver. The BIOS is also unique so that at boot time, the RAIDness of the subsystem will be properly managed. These implementations would be referred to as SW RAID. For solutions like Mylex, AMI/LSI, ServeRAID, the answer is that the algorithm is run on the Cards dedicated microprocessor thus it is termed a HW RAID solution. The real difference between the two IMHO is stability.

 

[computer]

FYI, software RAID is faster than hardware RAID when utilizing RAID 0 stripe. The fastest software RAID card is the Iwill SIDE RAID100 (among those tested). You only benefit from HW RAID when using RAID 5. More info