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Re: External log and possibilities.

To: "Martin K. Petersen" <mkp@xxxxxxxxxxxxx>
Subject: Re: External log and possibilities.
From: Steve Lord <lord@xxxxxxx>
Date: Fri, 20 Jul 2001 09:09:02 -0500
Cc: Keith Matthews <keith_m@xxxxxxxxxxxxxxxxxxx>, linux-xfs@xxxxxxxxxxx
In-reply-to: Message from "Martin K. Petersen" <mkp@xxxxxxxxxxxxx> of "20 Jul 2001 08:24:41 EDT." <yq166cnlree.fsf@xxxxxxxxxxx>
Sender: owner-linux-xfs@xxxxxxxxxxx
> >>>>> "Keith" == Keith Matthews <keith_m@xxxxxxxxxxxxxxxxxxx> writes:
> 
> >> I want wondering if anyone here was aware of non-volatile RAM
> >> devices 128m-1g and would such a device work with Linux and then
> >> allow you to use an external log to read/write to them.  I would
> >> expect that if it's based on SDRAM, etc it would make for some
> >> interesting performance gains.
> 
> >> Anyone have any thoughts on this?
> 
> Logging to NVRAM is quite common on other systems (Sun PrestoServe,
> Compaqdecital has one, NetApp, and most hardware RAID solutions).
> Unfortunately, good boards are both expensive and hard to come by.
> 
> I've tried to find one on several occasions, and I know Stephen
> Tweedie has done the same for his ext3 work.
> 
> Another option is to use a solid state disk.  But that will cost you
> an arm and a leg.

A quick hunt on google found this for one, no price without a phone call
though:

http://www.durabledata.com

and this web site:

http://www.emjembedded.com

actually has some prices, for a compact flash based 128M ide drive they
want $362. I could not find prices for anything non-flash based. Most
of these devices appear to be in the low Gbyte capacity and are several
thousand dollars each.

These people make solidstate disks:

http://www.soliddatasystems.com - no prices except in a press release
where they charge $9950 for a 536Mbyte drive! Basically this stuff is
expensive!

http://www.imperialtech.com - no prices or links to places you might
buy one from except the big guys (sun, emc, veritas ....).

The main problem appears to be that these are aimed at really high
end apps, not for being a filesystem journal.

Steve

p.s. At Cray we used to have SSDs which went forupto  several million dollars,
but they were static ram, large (for the time), VERY VERY fast, and this was
at least a decade ago.

> 
> 
> Keith> If you are talking about Flash then it has the limitation of a
> Keith> fairly small max numbr of write cycles. I have heard 100,000
> Keith> quoted - not much for a busy fileserver.
> 
> It is correct that flash has limitations - often in the order of
> magnitude you quote there.
> 
> However, NVRAM boards for logging use batteries to refresh regular
> memory, and consequently they don't suffer from the same problems.
> You need to get power back on the box within too long, though.  On
> most systems within a 2-3 day period.
> 
> 
> For people interested in experimenting with the performance gains from
> using a memory based log device, I recommend you put the log on a
> ramdisk (Only for testing. Kids, do not try this at home!).  
> 
> -- 
> Martin K. Petersen, Principal Linux Consultant, Linuxcare, Inc.
> mkp@xxxxxxxxxxxxx, http://www.linuxcare.com/
> SGI XFS for Linux Developer, http://oss.sgi.com/projects/xfs/



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