-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Thursday, 2010-01-28 at 17:17 -0500, Greg Freemyer wrote:
On Thu, Jan 28, 2010 at 4:38 PM, Carlos E. R. <> wrote:
Both do, AFAIK. Motherboard, bios raid, is not a real hardware raid, it needs a driver that does the real work in the cpu, with some help from the chipset. That's why it is called "fake raid".
I don't know the specifics, but mdraid for sure and possibly dmraid have been getting updates in the last year or so to offload the parity logic. I assume that some raid cards now expose their xor engine and thus the data blocks can be sent to them to handle the xor logic.
That would be interesting.
The patches I noticed were for IBM hardware iirc.
Then it is less interesting >:-)
I think the really big difference between dmraid and mdraid is compatibility. MS Windows only supports the equivalent of dmraid, so if you want to create a dual boot raid system, you need to go that way.
If Windows is not a concern, I think mdraid is the obvious choice but there may be some subtleties I don't know about.
What happens, I understand, is that the bios is capable of reading, and thus booting, from the fakeraid, which means that Windows is capable of booting. When the system is up, it loads the driver and gains write capability. This doesn't happen wit a linux software raid, we have to use tricks that allow grub or lilo to load the kernel first (like having /boot outside of the raid array). A better explanation, here: <http://en.wikipedia.org/wiki/Fakeraid#Firmware.2Fdriver-based_RAID_.28.22FakeRAID.22.29> Firmware/driver-based RAID ("FakeRAID") Operating system-based RAID doesn't always protect the boot process and is generally impractical on desktop versions of Windows (as described above). Hardware RAID controllers are expensive and proprietary. To fill this gap, cheap "RAID controllers" were introduced that do not contain a RAID controller chip, but simply a standard disk controller chip with special firmware and drivers. During early stage bootup the RAID is implemented by the firmware; when a protected-mode operating system kernel such as Linux or a modern version of Microsoft Windows is loaded the drivers take over. These controllers are described by their manufacturers as RAID controllers, and it is rarely made clear to purchasers that the burden of RAID processing is borne by the host computer's central processing unit, not the RAID controller itself, thus introducing the aforementioned CPU overhead from which hardware controllers don't suffer. Firmware controllers often can only use certain types of hard drives in their RAID arrays (e.g. SATA for Intel Matrix RAID, as there is neither SCSI nor PATA support in modern Intel ICH southbridges; however, motherboard makers implement RAID controllers outside of the southbridge on some motherboards). Before their introduction, a "RAID controller" implied that the controller did the processing, and the new type has become known by some as "fake RAID" even though the RAID itself is implemented correctly. Adaptec calls them "HostRAID". - -- Cheers, Carlos E. R. -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) iEYEARECAAYFAktiKysACgkQtTMYHG2NR9XmIQCfSh9yQJ5PHZq9OECspwpNvxou o+4Anih34LI8qMiWKjy3LXsPfDngdhzY =UdZk -----END PGP SIGNATURE----- -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org