On Fri, 13 Jul 2007, Justin Piszcz wrote:
You are using HW RAID then? Those numbers seem pretty awful for that
setup, including linux-raid@ even it though it appears you're running HW
raid, this is rather peculiar.
No, it has been discussed numerous times on this list.
SW raid is faster because it has access to (often) gigabytes of block
cache, which the HW raid controller doesn't have. SW raid is therefore
able to avoid a lot of reads when it needs to write, speeding things up
considerably.
I always use 3ware HW-raid though as I consider it more reliable. Since
most of my access is "write once, read many" write speed isn't as
important to me as data integrity.
Take your 3ware HW-raid, do a dd (read or write) to the device and see it
being very quick (because it can fit all the data into its cache as it
either reads or writes), then put a filesystem on it and do writes there,
especially journaled writes, and see write speed go down to 1/10 or so.
--
Mikael Abrahamsson email: swmike@xxxxxxxxx
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