Partition SSD and get full performance of each partition?

Discussion in 'iMac' started by zm15, Jul 8, 2015.

  1. zm15, Jul 8, 2015
    Last edited: Jul 9, 2015

    zm15 macrumors newbie

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    Jul 2, 2015
    #1
    If I partitioned my iMac (late 2014) 512GB SSD into 2 separate partitions in Yosemite, would I still get the normal write/read speeds of the drive on each partition?

    I'd like to put a video editing media cache on one partition, and the OS on the other. Curious if I'd get the 700MB read/write speeds on both partitions.
     
  2. yjchua95 macrumors 604

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    #2
    Yes you would. SSD is very different from HDD - in HDDs, the outer layer would be faster, and go slower as you progress inwards. Not in SSDs - performance is same throughout until it gets to the last 10% of the max capacity.
     
  3. kohlson macrumors 6502a

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    #3
    Theoretically, yes, depending on the load characteristics and the number of I/O channels on the SSD. But 700MB translates to roughly 7Gbps, which is faster than SATA 3.
     
  4. yjchua95 macrumors 604

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    #4
    And that's very possible on new Macs. I get about 1500MB/s in reads and writes on my mid-2015 13" rMBP.

    Newer Macs use PCIe SSDs, which can go way faster than SATA3.
     
  5. zm15 thread starter macrumors newbie

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    #5
    Interesting... Thanks for the input. So in theory, could you do a RAID 0 on a single physical drive with 2 partitions to increase speed? I'm thinking external SSD for media files.
     
  6. kohlson macrumors 6502a

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    #6
    Good catch by yjchua95 -- I didn't read your first post closely enough. I suspect that the SSDs used in Apple products are selected, at least somewhat, to be part of an end-to-end solution. But in any event you won't get faster throughput that the interface allows. PCIe is fast. If you are creating a setup where you have a partitioned SSD in an external enclosure, it won't go faster than the I/O port (such as USB3). But throughput can be faster, depending on the load characteristics and other aspects of the system architecture. For example, lots of small files may transfer at a speed closer to the I/O port maximum compared to a large file transfer. But this is why there are performance teams at most vendors. They try things out and see how they work, and what they can do to make a difference.
     
  7. yjchua95 macrumors 604

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    #7
    You can't RAID partitions on the same physical drive. There is no point of RAID-ing anyway, since the partitions all operate at the same speed.
     
  8. zm15 thread starter macrumors newbie

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    Jul 2, 2015
    #8
    So if I had 2 partitions on the same ssd drive, theoretically what would their transfer rate for files in folders transferred between them be since it wouldn't be going through the computer interface? Or would it? I.e. PCI-e internal connection to motherboard, but file transfer internal on the ssd. Perhaps I'm confusing myself...
     
  9. hfg macrumors 68040

    hfg

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    #9
    Disks can't do file transfers by themselves! Thus, your transfer rate would be the same (possibly even slower) than using 2 identical drives since the data still has to be read into memory, then written back out to the disk.
     

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