Subject: Re: Cheap RAM disk?
From: "Jeffrey W. Baker" <jwbaker@acm.org>
To: John A Meinel <john@arbash-meinel.com>
Cc: Postgresql Performance <pgsql-performance@postgresql.org>
In-Reply-To: <42E6661D.3060304@arbash-meinel.com>
References: <42E6661D.3060304@arbash-meinel.com>
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Date: Tue, 26 Jul 2005 10:42:19 -0700
Message-Id: <1122399740.12728.1.camel@toonses.gghcwest.com>
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On Tue, 2005-07-26 at 11:34 -0500, John A Meinel wrote:
> I saw a review of a relatively inexpensive RAM disk over at 
> anandtech.com, the Gigabyte i-RAM
> http://www.anandtech.com/storage/showdoc.aspx?i=2480
> 
> Basically, it is a PCI card, which takes standard DDR RAM, and has a 
> SATA port on it, so that to the system, it looks like a normal SATA drive.
> 
> The card costs about $100-150, and you fill it with your own ram, so for 
> a 4GB (max size) disk, it costs around $500. Looking for solid state 
> storage devices, the cheapest I found was around $5k for 2GB.
> 
> Gigabyte claims that the battery backup can last up to 16h, which seems 
> decent, if not really long (the $5k solution has a built-in harddrive so 
> that if the power goes out, it uses the battery power to copy the 
> ramdisk onto the harddrive for more permanent storage).
> 
> Anyway, would something like this be reasonable as a drive for storing 
> pg_xlog? With 4GB you could have as many as 256 checkpoint segments.

I haven't tried this product, but the microbenchmarks seem truly slow.
I think you would get a similar benefit by simply sticking a 1GB or 2GB
DIMM -- battery-backed, of course -- in your RAID controller.

-jwb