Re: RAID suggestions?
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On 03/18/08 17:21, Gregory Seidman wrote:
> On Tue, Mar 18, 2008 at 04:33:19PM -0500, Ron Johnson wrote:
>>
>> On 03/18/08 16:03, Damon L. Chesser wrote:
>>> Ron Johnson wrote:
>>>> On 03/18/08 15:41, Damon L. Chesser wrote:
>>>> [snip]
>>>>
>>>>> changes in HD tech). 6. I have seen dozens of catastrophic hardware
>>>>> controller failures with complete data lost and not one mdadm failure.
>>>>>
>>>> That just means you're using sucky hardware. We've been using h/w
>>>> controllers for 15 years, and never had a problem.
>>>>
>>>> Of course, they are proprietary, and from a Tier 1 vendor, cost a
>>>> lot of money, and maintenance fees are high.
>>>>
>>>> But we've never lost data from a controller failure. (And damned
>>>> little loss from any other reason, either, since there's a 24x7
>>>> admin staff that pays attention to drive failure lights, and
>>>> replaces them immediately.)
>>>>
>>> And that detailed care makes all the difference in the world! Now limp
>>> along with a drive failure, add a controller that needs updating and
>>> perform the update. Suddenly you find the meta data is "unstable" and
>>> you can not recover from it. I have NOT seen data loss from a
>>> professional, on the ball data center.
>> Well heck, no one who cares about his data would do that... You
>> replace the drive, let it rebuild, and *then* do the update.
>>
>> Or... don't buy sucky h/w in the first place. If you *really* care
>> about your data, you spend the extra bucks for quality h/w that has
>> a competent support staff behind it. And you pay for an adequate
>> backup solution!
>>
>> Otherwise, "you" are blaming on the h/w the sins of the humans who
>> bought the crummy h/w.
>
> See, here's the thing. That I in RAID is for inexpensive. The idea is to
> increase reliability on the cheap. You could engineer an amazing HD with a
No, it (was) to increase "single image" capacity. Small-capacity
hard drives were expensive, but high-capacity drives were *REALLY*
expensive. Much more expensive than simply the ratio of the
capacities would indicate. I.e., a 300MB drives was much more than
10x the price of a 30MB drive.
(Am I seriously dating myself?)
> MTBF rating of 150 years (hyperbole, but you get the point), but it would
> be hideously expensive. Unless you are using RAID to improve I/O rather
> than for redundancy, putting expensive hardware into the equation defeats
> the purpose of a RAID in the first place.
We used (and still use) RAID for it's redundancy and higher
bandwidth. We used it for it ability to create very large devices,
back when 36GB & 18GB were the norm. (And many of those devices are
still chugging along. DEC made damned fine hardware!)
> Since I don't have major I/O performance requirements, just redundancy
> requirements, I use software RAID. I probably always will. I know that even
> if 3ware (for example -- replace with the name of your favorite HW RAID
> manufacturer) goes out of business, my computer catches fire, and one of my
> mirrored drives dies, I can buy an off-the-shelf system, install Debian,
> and rebuild my RAID.
We (well, the company I work for) has much higher bandwidth needs
than that. Which is why all new purchases now use SANs. RAID 10
and a lot of cache makes a database really scream. Then it's only
the FC switch that's the potential bottleneck...
- --
Ron Johnson, Jr.
Jefferson LA USA
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