Re: The Small Company's Guide to Hard Drive Failure and Linux

["Derek Vadala" <derek () cynicism com>]

Frank Berger said:

> using RAID-1 is most of the times also okay as a software RAID
> configuration. Normally you do not see much more CPU load doing RAID 1
> as software...

CPU overhead has never really been the argument against software RAID-1.
Even with RAID-5, where it matters more, it's a forced argument at best.
The advantage of RAID-1 in hardware is that you are reducing the traffic
on the bus. In a two-disk hardware RAID-1, you send a single packet
(block) of data across your system buss and the controller replicates that
block out to the disks. With software RAID-1, you have two blocks flying
across the bus for every write. Maybe system bus saturation isn't
important to you and so then the point is moot.

As was pointed out earlier (but perhaps not with enough forcefulness)
nearly all hardware RAID controllers for ATA (IDE) are a lie. Unless you
are buying something high quality, what you are really getting is firmware
RAID-- software RAID on a chip. Who do you trust more to write a better
implementation of RAID? Neil Brown, who benefits from peer review, or some
anonymous software engineer at a motherboard manufacturer? In addition to
this, there is the tendency by these same vendors (many of whom provide
integrated motherboard support) to provide very badly written drivers that
hook into the SCSI layer-- making your array crawl.

On the other hand, SW RAID-1 is fast on Linux and if one side of your
mirror dies, you can bring up the remaining disks as a standalone device
(sans RAID)-- just mount the partitions normally. Presumably you aren't
worried about system bus saturation in this case, which I suspect 99/100
people are not.

Shameless plug (though it's getting a bit outdated):
http://www.oreilly.com/catalog/mraidlinux/index.html

Also let me second the endorsement of Pilosoft. They have been very
helpful through several power supply failures.


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