linux-kernel - Re: [PATCH] LogFS take three

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Date:	Sat, 19 May 2007 11:18:17 -0400
From:	Bill Davidsen <davidsen@....com>
To:	Dongjun Shin <djshin90@...il.com>
CC:	David Woodhouse <dwmw2@...radead.org>,
	Jörn Engel <joern@...ybastard.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mtd@...ts.infradead.org, Albert Cahalan <acahalan@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jan Engelhardt <jengelh@...ux01.gwdg.de>,
	Evgeniy Polyakov <johnpol@....mipt.ru>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Greg KH <greg@...ah.com>, Ingo Oeser <ioe-lkml@...eria.de>
Subject: Re: [PATCH] LogFS take three

Dongjun Shin wrote:

> There are so many flash-based storage and some disposable storages,
> as you pointed out, have poor quality. I think it's mainly because these
> are not designed for good quality, but for lowering the price.
> 
The reliability seems to be appropriate to the common use. I'm doubious 
that computer storage was a big design factor until the last few years. 
A good argument for buying large sizes, they are more likely to be 
recent design.

> These kind of devices are not ready for things like power failure because
> their use case is far from that. For example, removing flash card
> while taking pictures using digital camera is not a common use case.
> (there should be a written notice that this kind of action is against
> the warranty)
> 
They do well in such use, if you equate battery death to pulling the 
card (it may not be). I have tested that feature and not had a failure 
of any but the last item. Clearly not recommended, but sometimes 
unplanned needs arise.


> - In contrast to the embedded environment where CPU and flash is directly
> connected, the I/O path between CPU and flash in PC environment is longer.
> The latency for SW handshaking between CPU and flash will also be longer,
> which would make the performance optimization harder.
> 
> As I mentioned, some techniques like log-structured filesystem could
> perform generally better on any kind of flash-based storage with FTL.
> Although there are many kinds of FTL, it is commonly true that
> it performs well under workload where sequential write is dominant.
> 
> I also expect that FTL for PC environment will have better quality spec
> than the disposable storage.

The recent technology announcements from Intel are encouraging in that 
respect.

-- 
Bill Davidsen <davidsen@....com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot
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