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From: Ron Johnson on 13 Apr 2010 13:40
On 2010-04-13 11:13, thib wrote:
> Ron Johnson wrote:
>> On 2010-04-13 05:23, Jon Dowland wrote:
>>> Stan Hoeppner wrote:
>>>> If you're going to buy two
>>>> drives, you'd be stupid to not use mirroring for fault tolerance and a
>>>> little added read performance here and there (depends on application).
>>>
>>> I disagree. Mirroring only protects you against drive failures and not
>>> human error.
>>
>> And I disagree with that. Mirroring *definitely* makes both reads and
>> writes go faster, due to parallelism.
>
> Hmm. Don't ^ these.
>
> Backups are always necessary, mirroring is optional but speeds up
> recovery from hardware failure *only*. Sometimes, you can't backup (it
> doesn't make sense, it's too big, ..) and thus, yes, you also *need*
> mirroring (not just to speed up things). But it will not help you in
> case of human error, as Stan said.
>

Note that I didn't mention human error; probably should have snipped
out that part.

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From: Clive McBarton on 13 Apr 2010 16:40
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M.Lewis wrote:
> Would it be better to move the LVM to a larger SATA drive and migrate
> the boot drive on to a new small IDE HD? I've even thought to set it up
> to boot from a flash drive. Not sure that would be wise either.
>
> My question is is this a 'wise' thing. If not, why not and what would be
> the better approach?

Mike,

you didn't say how important speed is to you, and how large your wallet
is. If the answer to both is "very", you can think about getting 1 HD +
1 SSD (solid state disk). A decent SSD costs 3 times as much as a small
HD but will be more than twice as fast, hence faster than any RAID made
from 2 HDs, at least while reading. Reading probably matters to you most
since you talk about the boot drive. Writing speed on a decent SSD is
about as high as on a single HD.

A SSD is presumably the best (fastest) method to boot from. I assume
they qualify as flash drives. On the other hand, USB flash drives cannot
be particularly fast, unless you have USB 3.0 (hardly the case for your
computer, since it runs on a 250GB IDE HD). USB 2.0 limits the speed to
about 34MB per second, less than half the speed of a cheap HD.
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From: Stefan Monnier on 14 Apr 2010 14:50
>>> If you're going to buy two drives, you'd be stupid to not use
>>> mirroring for fault tolerance and a little added read performance
>>> here and there (depends on application).
>> I disagree. Mirroring only protects you against drive failures and not
>> human error.
> And I disagree with that.

With the fact that it's not necessarily stupid to not use mirroring?

> Mirroring *definitely* makes both reads and writes go faster, due
> to parallelism.

AFAIK that's not true for writes (they may even slow down slightly).
But in any case, this does not contradict the fact that the kind of
protection it offers is different from the one offered by using backup.


Stefan


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From: Ron Johnson on 14 Apr 2010 17:50
On 2010-04-14 13:40, Stefan Monnier wrote:
>>>> If you're going to buy two drives, you'd be stupid to not use
>>>> mirroring for fault tolerance and a little added read performance
>>>> here and there (depends on application).
>>> I disagree. Mirroring only protects you against drive failures and not
>>> human error.
>> And I disagree with that.
>
> With the fact that it's not necessarily stupid to not use mirroring?

Too many negatives, so I'll say it directly:

it is *smart* to use mirroring.

>> Mirroring *definitely* makes both reads and writes go faster, due
>> to parallelism.
>
> AFAIK that's not true for writes (they may even slow down slightly).
> But in any case, this does not contradict the fact that the kind of
> protection it offers is different from the one offered by using backup.
>

That is correct. No RAID protects against user stupidity.

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From: Stefan Monnier on 15 Apr 2010 01:50
>>>>> If you're going to buy two drives, you'd be stupid to not use
>>>>> mirroring for fault tolerance and a little added read performance
>>>>> here and there (depends on application).
>>>> I disagree. Mirroring only protects you against drive failures and not
>>>> human error.
>>> And I disagree with that.
>> With the fact that it's not necessarily stupid to not use mirroring?
> Too many negatives,

Looks like the problem indeed: you misunderstood Jon's objection
as well. It's the same old problem of people confusing "not (a => b)" as
"(not a) => (not b)".


Stefan


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