On Thu, August 21, 2014 3:54 pm, Matt wrote:
Hate to change the conversation here but that's why I hate hardware RAID.
I love hardware RAID. 3ware more than others. In case of hardware RAID it is tiny specialized system (firmware) that is doing RAID function. In the specialized CPU (I should have called it differently) inside hardware RAID controller. Independent on the rest of computer, and needing only power to keep going. Tiny piece of code, very simple function. It is really hard to introduce bugs into these. Therefore you unlikely will have problem on device level. To find the status of the device and its components (physical drives) you always can use utility that comes from hardware vendor, you can have even web interface if it is 3ware.
If it was software RAID, Linux would always tell you what's going on.
It does. And so does hardware RAID device. And most of them (3ware in particular) do not do offline (i.e. delaying boot) check/rebuild, but they do it online (they are being operational in degraded state, and do necessary rebuild with IO present on the device, they just export themselves to Linux kernel with the warning of being degraded RAID during boot).
Software RAID, however, has a disadvantage (more knowledgeable people will correct me wherever necessary). Software RAID function is executed by main CPU. Under very sophisticated system (linux kernel), as one of the processes (even if it is real time process), on the system that is switching between processes. Therefore, RAID task for software RAID lives in much more dangerous environment. Now, if it never finishes (say, kernel panics due to something else), you get inconsistent device (software RAID one), and it is much much much harder task to bring that to to some extent consistent state than, e.g., to bring back dirty filesystem that lives on the sane device. This is why we still pay for hardware RAID devices. I do.
Just my 2c.
Valeri
++++++++++++++++++++++++++++++++++++++++ Valeri Galtsev Sr System Administrator Department of Astronomy and Astrophysics Kavli Institute for Cosmological Physics University of Chicago Phone: 773-702-4247 ++++++++++++++++++++++++++++++++++++++++