Tracy Reed said:
On Mon, Jan 02, 2012 at 09:12:44AM -0500, Edward Ned Harvey spake thusly:
If it's in BIOS, then it's hardware. Below the OS, regardless of what OS you're talking about. Right? Or is there some new BIOS-vs-softwarestandard I'm not aware of?BIOS is software stored in memory mapped into the system's memory which is loaded into the CPU and executed.And that "hardware" RAID card? It contains memory. Which contains software. Which is loaded into a CPU (which happens to be much slower than your primary cpu with something like an 800Mhz PPC being typical) and executed. I've never understood the big deal about hardware RAID. Especially not while the vast majority of your primary CPU's time is most likely spent idling. More hardware to fail, expensive hardware to buy, incompatible on disk formats making RAID card failure very difficult, special drivers needed, differing commands and management tools needed for each RAID card... I stick with software RAID wherever possible.
the one thing that's key about hardware raid vs software raid is that good hardware raid cards have battery backed cache on the card.
This means that when the system looses power, they remember what has been written to the various drives, and if power comes back up 'soon enough' (usually measured in days), they can complete the writes with no data loss.
software raid, including the BIOS supported versions, don't have this, and store the data in the main system memory. If the system halts for any reason, you have no way of knowing what data got written to the drives and what didn't, this means that if you have a 7 disk raid 6 set, you can end up with 4 drives with one set of data and 3 drives with the prior set of data, and therefor no way of recovering either set of data.
now if you are just talking about the cheap cards that don't have battery backed memory on them, then you are still not going to be safe on power loss in any case, but you will still be better off than software raid for crashes and other things that don't cause the entire system to loose power because the card will complete the writes to the drives even if the main OS halts.
David Lang
On Mon, Jan 02, 2012 at 09:12:44AM -0500, Edward Ned Harvey spake thusly: > If it's in BIOS, then it's hardware. Below the OS, regardless of what OS > you're talking about. Right? Or is there some new BIOS-vs-software > standard I'm not aware of? BIOS is software stored in memory mapped into the system's memory which is loaded into the CPU and executed. And that "hardware" RAID card? It contains memory. Which contains software. Which is loaded into a CPU (which happens to be much slower than your primary cpu with something like an 800Mhz PPC being typical) and executed. I've never understood the big deal about hardware RAID. Especially not while the vast majority of your primary CPU's time is most likely spent idling. More hardware to fail, expensive hardware to buy, incompatible on disk formats making RAID card failure very difficult, special drivers needed, differing commands and management tools needed for each RAID card... I stick with software RAID wherever possible. -- Tracy Reed http://tracyreed.org Digital signature attached for your safety.
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