Where flash belongs

Where flash belongs

Summary: Putting flash into disk packaging, while convenient, is sub-optimal. Disk latency is so great that no one worries about adding a few hundred microseconds to an I/O.

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TOPICS: Hardware
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Putting flash into disk packaging, while convenient, is sub-optimal. Disk latency is so great that no one worries about adding a few hundred microseconds to an I/O. But once you've got low-latency storage those microseconds start to add up.

But I didn't really get the underlying advantage to low-latency I/O until I spoke to David Flynn, Fusion-io's CTO. He explained why reduced latency enhances system performance.

Sure, lower latency means faster I/Os, but the key is that fewer inflight I/Os frees up the CPU to do real work. Inflight I/Os eat up cache and create interrupts that chew up CPU cycles.

The Storage Bits take In short, this video is about why flash doesn't belong in disk drive packaging: flash's latency advantage is diluted for no good reason. Agree or not, if you are interested in the impact of flash on server architecture you will find David's discussion thought provoking.

Disks for capacity at low cost. Flash - on PCI-e or ExpressCard - for performance. Now if they'd just get a Mac OS version out!!!

Comments welcome, of course. Disclosure: Fusion-io paid me to make the video. My first reaction to their claims was skeptical but as I've learned more I've become a fan. Sadly, I have no stock in the company.

Topic: Hardware

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3 comments
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  • To replace floppy, CDs and DVDs

    Flash has very short write-life expectancy. So it's not suitable for hard disk replacement. If you have big capacicity flash, you won't be able to use to store many small files. It will burnt up the write limit quickly.

    So it will be usefule to copy large sized files only such CDs and DVDs.
    no nonsense
    • Write limit problem is solved?

      In looking at the Samsung SSD, if there is a write limit it has been solved or mitigated. Their SSD shows about 2 Million hours MTBF!

      Here is link where I got my info:

      http://www.samsung.com/global/business/semiconductor/products/flash/ssd/2008/what/overview.html
      howamil1
  • RE: Where flash belongs

    I don't know much about SSD but it would seem to me that, since he mentioned interrupts for SATA/SCSI then SSD must be an interlocked transfer. If so when going to flash as apposed to external storage, the CPU is busy for the entire request. That does not sound very efficient for a server.

    Also 10 microseconds is 100,000 IOPS. With hardware iSCSI, we were getting very close to 400,000 IOPS.
    eddyq