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Thread: RAID 0 vs RAPID mode with SSDs ?




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    Prevail's Avatar
    Prevail is offline Junior Member
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    Default RAID 0 vs RAPID mode with SSDs ?

    Samsung offers a RAM caching accelerator called "Rapid mode" which seems to markedly improve SSD performance, see review.
    I doubt this RAPID mode works in a RAID-0 configuration. So my question is whether a larger SSD with RAPID mode or two smaller SSDs in a RAID-0 would perform better?
    My second question is whether the Windows TRIM commands will work with SSDs in RAID-0? (I am running Win 8.1.)
    Thanks in advance for any advice.

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    parsec is offline Senior Member
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    Default Re: RAID 0 vs RAPID mode with SSDs ?

    Samsung's RAPID mode is a RAM disk-like feature that produces impressive results with benchmark test programs. That is caused by the your PC's RAM being tested, rather than the SSD itself.

    Some of the realities of RAPID:

    It is not running/working when the PC boots or restarts, so no improvement in boot/start up time.

    RAPID works only with some Samsung SSDs, and only one SSD may be in RAPID mode at a time. RAPID mode does not work with Samsung SSDs in a RAID array of any kind.

    The first time you read a file from the SSD (a PDF file for example), it will be read into the RAPID cache and also be sent to the PDF file display program. That happens at the SSD's standard speed, since the RAPID software does not automatically cache every (or any) file on the SSD. If you then close the PDF file reader, but later in the same Windows boot session, you open the same file again, it will be read from the RAPID RAM cache, of course at a much higher speed. That is, if it is still in the RAPID RAM cache.

    Since it uses your systems memory, which you choose how much to give to RAPID, its space is limited. Imagine you give RAPID 2GB of your RAM. As you and (if this SSD is the OS drive) the OS read files that are then put into the RAPID cache, it will become full at some point, and probably uses a first in first out, or usage count method of deciding what files are removed from the RAPID cache to make room for new ones. There is no guarantee a file will be in the RAPID cache.

    When you save/write a file to the RAPID enabled Samsung SSD, the file is written to the RAPID RAM cache, which happens very quickly, since you are "writing" to RAM memory. But that file still must be written to the permanent storage on the SSD, which is done at the standard write speed of the SSD.

    You can see that RAPID does not cause every file on a SSD in RAPID mode to be read at the speeds shown in a benchmark test of that SSD. It must be read into the RAPID cache before it will be available at the higher speeds. How can you cache 100GB of used space on a SSD into a 2GB RAPID RAM cache?

    IMO, to give the Samsung SSD credit for the performance of the RAM cache is just wrong. A RAM caching system like this could work with a standard HDD, or a USB flash drive. Seagate and Western Digital should have done this years ago. Samsung used RAPID to divert attention from the use of TLC NAND in the 840 EVO SSDs, and it worked perfectly. Plus they tweaked the actual performance of the 840 EVO in several ways to make it a better SSD, and in those aspects it is.

    On to RAID 0. RAID 0 increases disk IO performance in most aspects, except for small file, 4K random read speed. 4K random read speed is the major reason SSDs are so responsive compared to HDDs. The loss in 4K performance is not great, and the gains in other areas can be worth the tradeoff. But that depends upon what you are doing with the RAID 0 array. As an OS drive does it boot faster? No, but that is caused by the initial overhead of starting the RAID software. If you are reading and writing many large files a lot, then RAID 0 will be better than a single SSD. Or if your PC is bombarded with IO requests from whatever source, RAID 0 will have better performance than a single SSD.

    TRIM in RAID 0 works with Intel 7 series and newer chipsets, and IRST version 11 and greater drivers. Windows 8.1 TRIM works on those Intel platforms.

    RAPID and RAID are two very different things, the ways and aspects in which they increase performance are different. As always, what is better performance depends on what you are doing and what you want better performance to be. Only you can decide which one of these will provide better performance for you.

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