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A Look At BCache vs. LVM Cache For HDD+SSD Linux Systems

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  • A Look At BCache vs. LVM Cache For HDD+SSD Linux Systems

    Phoronix: A Look At BCache vs. LVM Cache For HDD+SSD Linux Systems

    For those thinking about potentially running a Linux system with a combination of SSD and HDD so that the solid-state drive would be able to act as a performance cache for commonly used data, BCache and LVM-cache/dmcache are two of the commonly used solutions...

    http://www.phoronix.com/scan.php?pag...M-Cache-Fedora

  • #2
    Nice!
    I 've always wanted to see some meaningful benchmarks of bcache vs lvm cache vs plain ssd.
    Been using bcache for my /home mountpoint for ages, it works great, but I never managed to test LVM cache myself.

    @Michael
    I would be very interested and grateful for such a benchmark.

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    • #3
      @Michael

      benchmarks would be very interesting.

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      • #4
        I once read that a better method than using some sort of cache, was to use ext4 on a spinning disk with external metadata, then place that metadata on an SSD. Has anyone else done this comparison? I suspect it's better for write-heavy workloads, in particular.

        Of interest with any of these solutions is how difficult they will be when the SSD hits write exhaustion. I know that SSDs are suppose to have a longer life than is supposed, but once you stick them into fast-turnover roles like caching, is that still true?

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        • #5
          Originally posted by phred14 View Post
          Of interest with any of these solutions is how difficult they will be when the SSD hits write exhaustion. I know that SSDs are suppose to have a longer life than is supposed, but once you stick them into fast-turnover roles like caching, is that still true?
          See this: http://techreport.com/review/27909/t...heyre-all-dead

          Even consumer level SSDs turn out to be much tougher than anyone gave them credit for.

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          • #6
            Yes please, and with more than just the default settings... Bcache has all sorts of settings to pass sequential IO to the spinning disk and such, so testing several different settings would be interesting.

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            • #7
              Is there a way to use an SSD as a cache for a RAID1 btrfs set up? Because I obviously don't want to do this at the block device level - that will cut the effective size of the cache by half. Of course, it would be best if the btrfs implementation handles this but since (AFAIK) it doesn't - is there some generic way to do it?

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              • #8
                Originally posted by ipso View Post
                Yes please, and with more than just the default settings... Bcache has all sorts of settings to pass sequential IO to the spinning disk and such, so testing several different settings would be interesting.
                Only if BCache upstream or elsewhere has out somewhere like a Wiki-based tuning guide, etc. Otherwise it becomes too time consuming and too unclear for others. That tends to be my requirement for most non-default testing is that there must be extensive documentation at length for tuning/performance tweaking.
                Michael Larabel
                http://www.michaellarabel.com/

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                • #9
                  I wonder also how it would handle on a USB drive instead of an SSD, a bit a la Windows ReadyBoost.

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                  • #10
                    Compatible with Windows in Dual-Boot

                    Is there any solution to use an SSD cache in a dual boot system for both systems efficiently?

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