[SLUG] Re: File Systems -- recovery with only a few sector errors ...

From: Bryan J. Smith (b.j.smith@ieee.org)
Date: Tue Sep 14 2004 - 18:41:13 EDT


On Tue, 2004-09-14 at 17:45, Chad Perrin wrote:
> When you say "standalone ATA", do you mean drives that are not part of a
> RAID?

Correct. Although it's all a mega-over-simplification.
Saying RAID is like saying 3D graphics.
Not only do you have varying level of hardware (if at all), but
different features.

When I think of "intelligent" RAID, I think of:
- On-board intelligence (microcontroller or ASIC)
- Rest of system cannot directly talk to ATA/SCSI controllers**
- GPL block driver for OS, all RAID functionality in firmware
- Sector reservation and automatic sector remapping
- Read load balancing over mirrors

Now some OS LVMs can do a lot of that. So it can be considered
"intelligent" RAID, even though it uses its own ATA channels.

In a nuthsell, the only negative solution is the FRAID (free RAID)
card. It puts the "brains" in software, and vendors don't make that
GPL. And the GPL implementation (ataraid.c) has yet to be supported by
_any_ FRAID vendors, so the resulting GPL vendor drivers (hptraid,
pdcraid.c, silraid.c) are not well supported.

> If so, I understand what you're saying. If not, I'd like some
> clarification.

I'm writing a FAQ on this among other things as of late:
  http://www.vaporwarelabs.com/

A FAQ is required because there are dozens upon dozens of technologies
and variable involved, just like with "Exchange replacements," just like
with "DVD burning" just like with "Network Services," etc...

-- 
Bryan J. Smith                                  b.j.smith@ieee.org 
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