In data mercoledì 27 gennaio 2021 04:11:31 CET, David C. Rankin ha scritto:
On 1/26/21 6:37 AM, Carlos E. R. wrote:
On 26/01/2021 01.27, David C. Rankin wrote:
On 1/25/21 4:07 PM, Markus Egg wrote:
Hello,
...
If this is windows on motherboard raid, it's probably dmraid (otherwise known as Fake RAID or BIOS RAID) -- it's not really Fake, it's just the moniker dmraid ended up with from the hardware RAID snobs...
It is really fake, because it doesn't run in hardware: it runs in software, on the computer CPU, with read support on BIOS so that it can boot. Once booted it gets write code from the driver, running on the mainboard CPU, not on the raid chipset.
A true hardware raid doesn't use the mainboard CPU, and is transparent to the operating system.
I'm sure Neil Brown and the rest on the linux-raid list would be surprised to learn it is fake...
It's software... (and the overhead ceased being measurable when 486 came out)
Fake is far superior to hardware. Just have a battery die on your hardware card and drop from write-back to write-through... and then find out your battery was discontinued 3 years ago. Now you have a hardware specific RAID install that can no longer benefit from the hardware write-back performance at all... Though, unless you are saturating whatever your setup is -- it really doesn't matter.
Not to mention that ZFS cannot be used fruitfully with hardware RAID. And actually, BIOS RAID is often limited to the Windows world as the producer do not invest in drivers for the kernel, that way the discs even if set as RAID in BIOS of the controller are seen as single discs (with the subsequent chaos). That said, for what I have seen, in a world were a controller can be just written off, you will then have recent hardware, were the argument "battery discontinued" is less valid. And if you go for high quality SAS discs, you will anyway end up with a "hard" RAID controller or at least with a hybrid one. Performance: I have two mdadm running here on a Phaenom board with TW and 32 GB of RAM and when you do video cut or similar, you do notice the limitations. But overall, for normal operations of office, I agree you do not. A question about "battery": is it still an argument if you system is backed up by an UPS? I thought the batteries on controller cards were paramount only on systems that are not protected by a convenient UPS. Wrong?