For best performance, the transaction log should be on a separate disk.

Does
the writing of the log benefit from a battery backed controller as
well? If not, what do people think about writing the transaction log
to a flash card or the like?

mbguy2000-1@yahoo.com wrote:
> For best performance, the transaction log should be on a separate disk.
>
> Does the writing of the log benefit from a battery backed controller
> as well? If not, what do people think about writing the transaction
> log to a flash card or the like?
How popular are the battery backed RAM drives that exist today? I don't
recall seeing them spoken about in this mailing list. The local geek
shop has these devices on sale. Are they still too expensive?

For those that don't know what I am talking about - they are PCI devices
that present themselves as a hard drive, but are filled with commodity
RAM instead of a magnetic platter, and a battery that lasts a few weeks
without external power.

Cheers,
mark

--
Mark Mielke <mark@mielke.cc>

On Aug 29, 2007, at 12:54 PM, Mark Mielke wrote:

> mbguy2000-1@yahoo.com wrote:
>> For best performance, the transaction log should be on a separate
>> disk.
>>
>> Does the writing of the log benefit from a battery backed
>> controller as well? If not, what do people think about writing
>> the transaction log to a flash card or the like?
> How popular are the battery backed RAM drives that exist today? I
> don't recall seeing them spoken about in this mailing list. The
> local geek shop has these devices on sale. Are they still too
> expensive?
>
> For those that don't know what I am talking about - they are PCI
> devices that present themselves as a hard drive, but are filled
> with commodity RAM instead of a magnetic platter, and a battery
> that lasts a few weeks without external power.

It think the general conclusion was "When they come out with an ECC
version, we'll look at them."

There are higher end ones that do have ECC RAM (and backup drives and
stuff) but they're spectacularly more expensive than the cheapo
consumer ones.

Cheers,
Steve




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On Wed, Aug 29, 2007 at 01:11:32PM -0700, Steve Atkins wrote:
> It think the general conclusion was "When they come out with an ECC
> version, we'll look at them."

FWIW, it shouldn't be impossible to implement ECC in software; they'd still
be orders of magnitude faster than normal disks.

/* Steinar */
--
Homepage: http://www.sesse.net/

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In response to Mark Mielke <mark@mark.mielke.cc>:

> mbguy2000-1@yahoo.com wrote:
> > For best performance, the transaction log should be on a separate disk.
> >
> > Does the writing of the log benefit from a battery backed controller
> > as well? If not, what do people think about writing the transaction
> > log to a flash card or the like?

Flash cards write _very_ slowly.

> How popular are the battery backed RAM drives that exist today? I don't
> recall seeing them spoken about in this mailing list. The local geek
> shop has these devices on sale. Are they still too expensive?

I've seen them around and as best I can tell, they're pretty
inexpensive. The main drawback is the storage, you'd be looking at
the price of the card, plus the price of however much RAM you wanted
on it.

http://www.amazon.com/Gigabyte-GC-RA...8418613&sr=8-1
http://techreport.com/articles.x/9312/1
Up to 4G, but you have to add the price of the RAM on to the price of
the card.

In the case of WAL logs, you could probably get away with a lot less
space than many other usages, so they might be very practical.

--
Bill Moran
Collaborative Fusion Inc.
http://people.collaborativefusion.com/~wmoran/

wmoran@collaborativefusion.com
Phone: 412-422-3463x4023

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On Wednesday 29 August 2007, Steve Atkins <steve@blighty.com> wrote:
> There are higher end ones that do have ECC RAM (and backup drives and
> stuff) but they're spectacularly more expensive than the cheapo
> consumer ones.
>

Yeah the good ones look more like http://ramsan.com/ .

--
"Pulling together is the aim of despotism and tyranny. Free men pull in
all kinds of directions." -- Terry Pratchett


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