On 05/28/2015 03:02 PM, Valeri Galtsev wrote:
If I get you correctly you are saying that 3ware RAID cards are prone to
hardware failures - as opposed to software RAID which is not (as it does
not include hardware, so never has a hardware failures), right? No this is
a joke of course. But it's the one one asked for ;-)
Software RAID uses whatever controller the disks are connected to.
Often, that's the AHCI controller on the motherboard. And those
controllers are almost always more reliable than 3ware. Seriously. No
joke.
Again, I don't know your statistics: i.e. how many did you use,
Hundreds of systems, both with 3ware and with software RAID.
how many
of them died (failed as hardware).
Not many, but some. A handful of data corruption cases (maybe 5? I
don't have logs). One BBU failure that resulted in a system that
wouldn't boot until it was removed (and a couple of hours down time
while 3ware techs worked that ticket). A couple of times when we really
wanted to move an array of disks and couldn't.
Vs zero reliability issues with software RAID.
How well surge-free the power is.
We always used trusted UPS hardware.
How
well the guys who installed your cards into your boxes followed static
discharge precautions
Our systems were built by a professional VAR. Employees always wore
ground straps. There were other anti-static measures in place as well.
I had been to the facility.
And I'll throw you a curveball:
I've argued that software RAID is more reliable than 3ware cards,
specifically. In the world of ZFS and btrfs, you absolutely should not
use hardware RAID. As you mentioned earlier, hardware RAID volumes
should scan disks regularly. However, scanning only tells you if disks
have bad sectors. It can also detect data (parity) errors, but it can't
repair them. Hardware RAID cards don't have information that can tell
them which sectors are correct. ZFS and btrfs, on the other hand,
checksum their data and metadata. They can tell which sectors are
damaged in the case of corruption such as bit flips, and which sector
should be used to repair the data.
Now, btrfs and ZFS are completely different from software RAID. I'm not
comparing the two. But hardware RAID simply has too many deficiencies
to justify its continued use. It should go away.
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