Valeri,
I hope you realize that your arguments for hardware RAID
all depend on everything working just right.
If something goes wrong with a disk (on HW RAID)
you can't just simply take out the disk, move it to another
computer and maybe do some forensics.
The formatting of disks on HW RAID is transparent to Linux.
Therefore my disks are all RAID or not.
What if I wanted to mix and match? Maybe I don't want my swap
RAID for performance.
The idea of taking my data (which is controlled by an OSS
Operating System, Linux) and putting it behind a closed source
and closed system RAID controller is appalling to me.
It comes down to this: Linux knows where and when to position
the heads of disks in order to max performance. If a
RAID controller is in the middle, whatever algorithm
Linux is using is no longer valid. The RAID controller
is the one who makes the I/O decisions.
Sorry, this is not something I want to live with.
GKH
>
> 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
> ++++++++++++++++++++++++++++++++++++++++
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