<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><span class="Apple-style-span" style="font-family: Times; font-size: 16px; "><pre style="font-size: 11px; ">Maciej,</pre><pre style="font-size: 11px; ">MRAM would be suitable for this. Freescale Semi spun off their MRAM unit recently, but they're shipping small (but expensive) MRAM chips. </pre><pre style="font-size: 11px; ">-Timothy </pre><pre style="font-size: 11px; "><br></pre><pre style="font-size: 11px; "><blockquote type="cite">The real problem here is that this is going to be a constantly written
16 bytes of nvram.
This will _very_ very quickly kill any type of flash that I'm aware
of... as such it would have to be something
along the lines of a battery backed few KB of ram, with write out to
flash on failure.
Not sure what the lifetime in write-cycles of the standard cmos nvram
is, but even if (being battery backed)
it would work, that's a real hard place to find any space...?
Maciej
On Sun, Jul 27, 2008 at 14:29, Daniel Phillips <<a href="http://tux3.org/cgi-bin/mailman/listinfo/tux3">phillips at phunq.net</a>> wrote:
><i> Hi Timothy,
</i>><i>
</i>><i> On Sunday 27 July 2008 14:10, timothy norman huber wrote:
</i>>><i> Daniel,
</i>>><i>
</i>>><i> Several weeks ago, during a discussion over coffee, you mentioned a
</i>>><i> rather intriguing optimization- by writing the start of the forward
</i>>><i> log chain to NVRAM rather than disk, you avoid a disk seek and write
</i>>><i> transfer for each forward log chain. i believe there was another
</i>>><i> motivation that had to do with avoiding traversing the entire volume
</i>>><i> in case of a crash. Was this design feature to overcome lame fsck
</i>>><i> performance?
</i>><i>
</i>><i> The same motivation, actually. Writing the start of a forward log
</i>><i> chain to nvram instead of to some known location on disk means that I
</i>><i> do not have to worry about doing unnatural things to optimize such
</i>><i> loads as O_SYNC writing, where each transaction has to complete
</i>><i> before the next one can begin, which means that the forward log chain
</i>><i> never gets more than one element log, requiring a seek to the known
</i>><i> location for every transaction. Not worse than journalling to be
</i>><i> sure, and usually better, but not as fast as avoiding a seek and disk
</i>><i> write per transaction entirely.
</i>><i>
</i>><i> So if somebody could give me 16 bytes of NVRAM or so per volume I
</i>><i> would be most pleased and could use that to generate some nice O_SYNC
</i>><i> benchmarks :-)
</i>><i>
</i>><i> By the way, I wonder why your posts do not show up in the Mailman
</i>><i> (Pipermail) archive, while mine and Matt's do?
</i>><i>
</i>><i> Daniel</i></blockquote></pre></span></div><div style="font-size: 8px; "><br style="font-size: 8px; "></div><br style="font-size: 8px; "><div apple-content-edited="true"> <span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><font class="Apple-style-span" face="Arial"><font class="Apple-style-span" color="#373848">Timothy Huber</font></font><div><font class="Apple-style-span" face="Arial"><font class="Apple-style-span" color="#373848">Strategic Account Development</font></font></div><div><font class="Apple-style-span" face="Arial"><font class="Apple-style-span" color="#373848"><br></font></font></div><div><font class="Apple-style-span" face="Arial"><font class="Apple-style-span" color="#373848"><a href="mailto:tim.huber@metaram.com">tim.huber@metaram.com</a></font></font></div><div><font class="Apple-style-span" face="Arial"><font class="Apple-style-span" color="#373848">cell 310 795.6599</font></font></div><div><br></div><div><span class="Apple-style-span" style="color: rgb(80, 97, 108); font-family: Arial; line-height: 16px; "><span class="Apple-style-span" style="color: rgb(0, 0, 0); font-family: Helvetica; line-height: normal; "><a href="http://www.metaram.com/">MetaRAM Inc.</a></span></span></div><div><span class="Apple-style-span" style="color: rgb(80, 97, 108); font-family: Arial; line-height: 16px; ">181 Metro Drive, Suite 400 </span></div><div><span class="Apple-style-span" style="font-family: Times; font-size: 16px; "><span class="mainText2" style="color: rgb(80, 97, 108); font-family: Arial, Helvetica, sans-serif; font-size: 12px; line-height: 16px; ">San Jose, CA 95110 </span></span></div><div><font class="Apple-style-span" color="#50616C" face="Arial"><span class="Apple-style-span" style="line-height: 16px; "><br></span></font></div><div><font class="Apple-style-span" color="#50616C" face="Arial"><span class="Apple-style-span" style="line-height: 16px; "><a href="http://www.linkedin.com/in/timhuber">http://www.linkedin.com/in/timhuber</a></span></font></div></div></div></div></div></div></div></div></span></div></span> </div><br></body></html>