Tape is Dead Disk is Tape Flash is Disk RAM Locality is King
Tape is Dead Disk is Tape Flash is Disk RAM Locality is King Jim Gray Microsoft December 2006 Tape Is Dead Disk is Tape 1TB disks are available 10+ TB disks are predicted in 5 years Unit disk cost: ~$400 ~$80 But: ~ 5..15 hours to read (sequential) ~15..150 days to read (random)
Need to treat most of disk as Cold-storage archive FLASH Storage? 1995 16 Mb NAND flash chips 2005 16 Gb NAND flash Doubled each year since 1995 Market driven by Phones, Cameras, iPod, Low entry-cost, ~$30/chip ~$3/chip 2012 1 Tb NAND flash Samsung prediction == 128 GB chip == 1TB or 2TB disk for ~$400 or 128GB disk for $40
or 32GB disk for $5 FLASH Some Parameters 5,000 IO/s per chip! Chip read write ~ 20 MB/s ~ 10 MB/s N chips have N x bandwidth Latency ~ 25 s to start read, ~ 100 s to read a 2K page ~ 2,000 s to erase ~ 200 s to write a 2K page
Power ~ 1W for 8 chips and controller Whats Wrong With FLASH? Expensive: $/GB 50x more than disk today Ratio may drop to 10x in 2012 Limited lifetime ~100k to 1M writes / page requires wear leveling but, if you have 1B pages, then 15,000 years to use the pages. Slow to write you can only write 0s, so erase (set all 1) then write.
Obvious Uses For Flash PDAs, cameras, iPod, . Laptop disks power, rugged, quiet, big enough, Not so obvious use: ARCHIVE for photo/music/.. because its simple to understand. Enterprise drives (lots of IO/s per $ per watt per liter ) One Could Make a Flash Disk (or a Flash File System) 6K random reads/sec, 3K random writes/sec
The IO capacity of 30..45 disks Uses 1 W vs 500W replace with 1 Less space, 10TB disk and 3 FLASH disks See A Design for High-Performance Flash Disks Birrell, Isard, Thacker, Wobber MSR-TR-2005-176
We Are Not There Yet Current FLASH disks could do much better on writes (100x better (!)) Algorithms are known but This changes many ratios Access time is 20x less (~200us) IOps is 100x more Re-evaluate page sizes MSR-TR-2006-168 FlashDB: Dynamic Self-tuning Database for NAND Flash, Suman Nath, Aman Kansal RAM Locality is King Storage Price vs Time The cpu mostly waits for RAM KB/$
Flash / Disk are 100:1 Disk 100,000 1,000,000 RAM clocks away from cpu RAM is ~100 clocks away unless you have locality (cache). If you want 1CPI (clock per instruction) 10 years you have to have the data in cache (program cache is easy ) This requires cache conscious data-structures and algorithms sequential (or predictable) access patterns Main Memory DB is going to be common.
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