On 9/21/12 8:41 AM, "Hearns, John" <john.hea...@mclaren.com> wrote:
> > >Are your concerns about the accuracy of this statement related to the >fact that elReg is claiming that they must dump "the entire memory" or >some concern about flash being used as a temporary checkpointing medium? > >The "entire memory" statement puzzled me. > >But using flash in this fashion does seem a good idea. Flash is slow, though... SLC NAND flash (pretty fast, 8 Gbit part) is 250 microseconds to write a 4kbyte (approx) page. Erasing is about 700 microseconds (reading is 25 microseconds) MLC flash (say 512Gbit parts with 8 kBbyte pages) takes 1.3milliseconds to write a page, 3.8 ms to erase (75us to read)... And has a life of 3000 write/erase cycles. That's 53 Mpbs streaming to the part. Yeah, any practical design is going to have multiple interleaved devices, etc. so you can probably do it faster.. But still, say you are checkpointing 8Gbyte.. That's 1300 seconds (yep, about 20 minutes), assuming you've previously erased everything. Even if you use the really fast SLC NAND, you're still looking at 500 seconds. You might be able to do it faster to a good hard disk with optimized data flow. Fast compared to disk, maybe, but very slow. Why not just mirror memory (other than cost and power: RAM is much less dense than flash) There's also the write cycle limit.. If you're looking for very high densities (USB thumb drive) you're looking at A) serial interfaces B) MLC NAND with maybe 10k cycle life on each page > >The contents of this email are confidential and for the exclusive use of >the intended recipient. If you receive this email in error you should >not copy it, retransmit it, use it or disclose its contents but should >return it to the sender immediately and delete your copy. >_______________________________________________ >Beowulf mailing list, Beowulf@beowulf.org sponsored by Penguin Computing >To change your subscription (digest mode or unsubscribe) visit >http://www.beowulf.org/mailman/listinfo/beowulf _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org sponsored by Penguin Computing To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
