Samsung SSD RAID0

Discussion in 'Mac Pro' started by El Awesome, Aug 29, 2012.

  1. El Awesome, Aug 29, 2012
    Last edited: Aug 29, 2012

    El Awesome macrumors 6502

    El Awesome

    Joined:
    Jul 21, 2012
    Location:
    Zurich
    #1
    Hey guys,

    I got 2 128GB Samsung 830 SSDs.
    I'm not sure if I should keep them seperate or put them in a RAID0.
    Some guys in the internet said that the speed increase from raiding SSDs is very small, but since my Mac Pro 4.1 only got SATAII built-in, I guess that's a different story?
    I don't want to got via Velocity Solo X2, mainly because here in Switzerland it's not available. I'd have to go via Amercia, which doubles the price for me. And then I heard that going via PCIe increases the boot time.

    I want to throw my system (boot disk) and app on it. Then, I want to make a little Bootcamp partition where I have (maybe) BF3 installed (to load maps faster and stuff...). 256GB are enough anyway.

    I know that with RAID0 SSDs have a shorter life, but I have a backup and 3 years warranty anyway.
    Help would be appreciated! Thx!

    Alex
     
  2. deconstruct60 macrumors 604

    Joined:
    Mar 10, 2009
    #2
    If going to merge , RAID 0, and then partition the two disks ...... why not just install Mac OS X on one and Windows on the other.

    If you need to store several large apps (e.g., bulky games ) on the Windows disk you'll have room. Similarly if want to later have a dual boot Win7 Win8 set up again there is room. It isn't a good thing to fill the SSD up to the brim. RAID 0 would distribute the storage across the two, but just having two (or more volumes) does the same thing.

    Unless have a demonstrated huge block in I/O throughput on a single SSD going to RAID 0 is showboating than anything else.


    Not necessarily. If running at normal write rates the lifetime would be longer; not shorter. If writing out 1TB/day then RAID0 over two disk won't make that much of a difference. What is killing the disks off is all the writing. Typically folks who have enormous amounts of data to write want to write faster. They'll choose RAID 0 , 5, 10, etc but the root cause is the amount of writing. If primarily spend most time reading there is no impact.
     
  3. El Awesome thread starter macrumors 6502

    El Awesome

    Joined:
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    Location:
    Zurich
    #3
    That makes sense.
    The thing is that I use OS X 90% of the time, so I rather keep Win7 completely on a different HD and Raid my SSDs.

    I still wonder about the increase of speed I would get from RAID0?

    But thanks for pointing out!
     
  4. deconstruct60 macrumors 604

    Joined:
    Mar 10, 2009
    #4
    The "problem" will be once you have gotten used to running OS/Apps on a SSD that 10% of the time on HDD based Win7 will be annoying.

    If need a relatively small "scratch work" space then could partition half of the "Win7" SSD to being a scratch HFS+ formatted partition.


    If using other Mac Pro drive sleds to do significant I/O against HDDs then probably not much. if on HDD now the jump to even a single SSD is substantial. You could squeeze out a bit better on benchmarks with RAID 0 but it isn't going to be as large of a jump as made from HDD based operations. Percentage wise it will be much smaller increase.

    SATA II isn't so much the issue as swaping the SATA controllers. With 6 SATA II links coming in there is no where near that much bandwidth going "out" (to the rest of the computer). Two SSDs at about max SATA II capacity is about enough to swamp the controller. SATA isn't designed for devices that operate at the rated speeds of the conduites ( 3Gb/s , 6Gb/s , etc.). It is designed for devices that operate substantially slower and the data is aggregated into these faster speeds.
     
  5. El Awesome thread starter macrumors 6502

    El Awesome

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    #5
    Makes sense. Thanks.
     
  6. ColdCase, Aug 29, 2012
    Last edited: Aug 29, 2012

    ColdCase macrumors 68030

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    #6
    You could get plenty of discussion here as the answer depends on what you are using the computer for and how well those SDs perform behind a RAID.

    In a workstation type environment, there may be little perceived difference in read performance between a pair of SSDs in a RAID0 configuration over two separate drives. You should think about RAID0 only if you need raw data rate. If you need a "large" drive capacity, think about concatenating them into a JBOD.

    There are a couple of things to think about with RAIDing SSDs. First, does Samsung recommend putting that model behind a RAID, what are others seeing in performance when RAIDing that specific SSD model. The SSD memory architecture and controller code could behave poorly.

    Writing flash memory takes much more time than reading and has a tendency to wear out gates. Some controllers, Sandforce in particular, use data compression to reduce the number of writes needed to store data which, in effect, improves perceived write speeds and reduces wear. Different controllers use different strategies and some just don't do well behind a RAID. RAID0 will make the data look more random to the SSD controller, for example, so compression is not as effective and you are back to slow writes (still faster than HDs).

    With standard files you may not see as much write performance increase to make it worthwhile. Remember, with RAID0 striped, one drive fails you loose everything on both drives.

    IMHO, if you need a large capacity drive to partition, concatenated the drives. The downsides of RAID0 risks on you boot drive and standard data files makes it hardly worth it. There are environments where its worthwhile, however.

    I do use RAID0 for video capture, where I need all the write data rate I can get, but my boot and APP drives are always non-RAIDed.
     
  7. 666sheep macrumors 68040

    666sheep

    Joined:
    Dec 7, 2009
    Location:
    Poland
    #7
    RAIDing SSD for booting and apps is pointless. Especially current ones. Speed gain won't be even noticeable, unless you'll be writing big amount of large files (what isn't often on a boot drive). Not to mention MP SATA limitations.

    I'd suggest (follow deconstruct60's advice) one for OS X, second one for Win. No Bootcamp needed.
     
  8. deconstruct60 macrumors 604

    Joined:
    Mar 10, 2009
    #8
    It is more likey the RAID controller ( hardware and a bit less so software implemented) will behave badly. HDDs tend to be faster writers than readers. It is exactly the opposite with SDDs. If the RAID controller has preconcieved notions how storage devices behave it will assume the SSD is broken when it isn't.

    The other problem RAID controllers present is that tend to block "meta" SATA commands from going downstream to the individual devices. The don't do SMART data ( usually another interface to get overall summary) and don't do things like Secure Erase and TRIM. Usually also an issue for firmware updates.

    If have a SSD that needs TRIM then it is generally an issue. In a Mac OS X context though there usually isn't any TRIM commands for non Apple drives. So not missing out.

    Those corner cases are where it is usually better to feed that kind of throughput into/"out of" yet another SATA controller. For example, effectively get another one when use a PCI-e SSD card.

    But yes that isn't OS/Apps/normal usage; even for a SSD.
     
  9. ColdCase, Aug 29, 2012
    Last edited: Aug 29, 2012

    ColdCase macrumors 68030

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    #9
    Yeah, I think I've confused the audience here by simply saying controllers. There are SATA controllers on the logic board (or in PCI slots) that have SATA interfaces (s) on one side and CPU interfaces on the other.

    I meant the memory controller within the SSD device itself, the controller that has SATA on one side (presents SATA to the host computer) and flash memory chips on the other.

    Sorry.

    And to get a clear picture of where the bottlenecks may be, an understanding of how all the controllers work is necessary.
     

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