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Results: A PCIe SSD's Random Performance

A 1400 MB/s SSD: ASRock's Z97 Extreme6 And Samsung's XP941
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Random performance is another issue entirely. We already know that throughput ceilings aren't as much of a concern when it comes to moving around lots of small chunks of data. In fact SATA 6Gb/s is typically sufficient for heavy random workloads. 

The Samsung XP941 employs AHCI, which has some inherent overhead that chokes the potential of solid-state storage. NVMe was designed to address this. However, Intel's NVMe driver isn't expected until the end of 2014. As a result, we have to accept that a PCIe-based SSD utilizing AHCI is probably going to demonstrate modest advantages, at best. How does the XP941 stack up in the two different connectors exposed by ASRock's Z97 Extreme6?

Random Read Performance

Given what we saw on the previous page, it'd be easy to assume that Samsung's XP941 is capable of massive transactional performance working with small random transfers. The truth is a matter of relativity.

Yes, 120,000 IOPS is an impressive result. But that number doesn't reflect the potential of Samsung's hardware the same way sequential transfers do. And yes, the four-lane Ultra M.2 slot does yield better results. However, the scaling isn't there to indicate that a two-lane interface attached to the PCH was really hamstrung, either.

Even more telling, the two- and four-lane interfaces track alongside the SATA 6Gb/s-based 840 Pro up until a queue depth of 16. Desktop workloads typically don't see that much concurrency, so the XP941 wouldn't confer much benefit.

Random Write Performance

This is mostly what I would have expected based on our previous work with PCIe-based SSDs utilizing AHCI. The SATA-attached 840 Pro takes top honors, even if it isn't the fastest SSD around. Samsung's XP941 falls flat connected to the two-lane M.2 slot. It fares better when we hook up with the four-lane Ultra M.2 interface, though not in any way that'd lead us to favor such a configuration over familiar SATA. 

Bottom line: the random performance of a PCIe-based SSD is more pedestrian than the impressive sequential scores, largely due to AHCI. Still, if you stopped here and didn't look at any other benchmark, you might conclude that Samsung's XP941 is the greatest desktop-oriented SSD ever. But our testing in Iometer isn't necessarily indicative of how the drive behaves in the real world. We need to go into more depth.

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  • -7 Hide
    aminebouhafs , June 5, 2014 5:16 AM
    Once an SSD in plugged into the Ultra M.2 slot, the bandwidth between central processing unit and graphics processing unit is cut-down by half. Therefore, while the end-user gets additional SSD performance, the end-user may lose some GPU performance because of insufficient bandwidth between it and the CPU.
  • 8 Hide
    JoeArchitect , June 5, 2014 7:18 AM
    Very interesting article and a great read. Thanks, Chris - I hope to see more like this soon!
  • 0 Hide
    wussupi83 , June 5, 2014 8:21 AM
    great article! - although z97 still seems boring
  • -1 Hide
    Eggz , June 5, 2014 9:54 AM
    This makes me excited for X99! With 40 (or more) lanes, of PCI-e (probably more), there will be no need to compromise. We have to remember that the Z97 Chipset is a consumer-grade product, so there almost has to be tradoffs in order to justify stepping up to a high-end platform.

    That said, I feel like X99, NVMe, and and M.2 products will coincide nicely with their respective releases dates. Another interesting piece to the puzzle will be DDR4. Will the new storage technology and next-generation CPUs utilize it's speed, or like DD3, will it take several generations for other technologies to catch up to RAM speeds? This is quite an interesting time :) 
  • 5 Hide
    Amdlova , June 5, 2014 9:56 AM
    Chris test the asrock z97 itx... and another thing... my last 3 motherboard from asrock and i want to say Asrock Rock's!
  • 0 Hide
    Damn_Rookie , June 5, 2014 11:27 AM
    While storage isn't the most important area of computer hardware for me, I always enjoy reading Christopher's articles. Very well written, detail orientated, and above all else, interesting. Thanks!
  • 0 Hide
    hotwire_downunder , June 5, 2014 8:58 PM
    ASRock has come along way, I used them a long time back with disappointing results, but I have started to use them again and have not been disappointed this time around.

    Way to turn things around ASRock! Cheap as chips and rock steady!
  • 0 Hide
    alidan , June 5, 2014 10:51 PM
    @aminebouhafs if i remember right, didn't toms show how much performance loss there is when you tape gpu cards to emulate having half or even a quarter of the bandwidth? if i remember right back than the difference was only about 12% from 16 lanes down to either 4 or 8
  • 1 Hide
    Eggz , June 6, 2014 7:39 AM
    Quote:
    @aminebouhafs if i remember right, didn't toms show how much performance loss there is when you tape gpu cards to emulate having half or even a quarter of the bandwidth? if i remember right back than the difference was only about 12% from 16 lanes down to either 4 or 8


    PCI-e 3.0 x8 has enough bandwidth for any single card. The only downside to using PCI-e lanes on the SSD applies only to people who want to use multiple GPUs.

    Still, though, this is just the mid-range platform anyway. People looking for lots of expansion end up buying the X chipsets rather than the Z chipsets because of the greater expandability. I feel like the complaint is really misplaced for Z chipsets, since they only have 16 PCI-e lanes to begin with.
  • 2 Hide
    cryan , June 8, 2014 5:22 AM
    Quote:
    Once an SSD in plugged into the Ultra M.2 slot, the bandwidth between central processing unit and graphics processing unit is cut-down by half. Therefore, while the end-user gets additional SSD performance, the end-user may lose some GPU performance because of insufficient bandwidth between it and the CPU.


    Well, it'll definitely negate some GPU configurations, same as any PCIe add-in over the CPU's lanes. With so few lanes to work with on Intel's mainstream platforms, butting heads is inevitable.

    Regards,
    Christopher Ryan


  • 3 Hide
    cryan , June 8, 2014 5:23 AM
    Quote:
    While storage isn't the most important area of computer hardware for me, I always enjoy reading Christopher's articles. Very well written, detail orientated, and above all else, interesting. Thanks!


    Awww, shucks!

    Regards,
    Christopher Ryan
  • -1 Hide
    obamaliar , June 8, 2014 12:08 PM
    Supercool review, Just as a note though any pair of good SATA Based SSD's will blow the doors off of that x941. For example I am getting 740.00MB/s bandwidth at steady 5 and 948.37MB/s at recovery 5 for PCM8 extended photoshop heavy from a pair of Intel 730's
  • -1 Hide
    obamaliar , June 8, 2014 12:10 PM
    Supercool review, Just as a note though any pair of good SATA Based SSD's will blow the doors off of that x941. For example I am getting 740.00MB/s bandwidth at steady 5 and 948.37MB/s at recovery 5 for PCM8 extended photoshop heavy from a pair of Intel 730's
  • 1 Hide
    Evolution2001 , June 8, 2014 8:08 PM
    obamaliar, how do you reckon that your 740MBps or 948MBps is faster than 1400MBps? (referencing the sequential read of the tested drive)
    SATA3 has a theoretical max of 6Gbps (750MBps). However, the practical max is more around 600MBps.
    Assuming you are running your Intel 730's in RAID-0 and achieving the max practical throughput, you'd still only come up with ~1200MBps which is slower than what Tom's saw at 1400MBps ON A SINGLE DRIVE.
  • -1 Hide
    obamaliar , June 9, 2014 8:55 AM
    Quote:
    obamaliar, how do you reckon that your 740MBps or 948MBps is faster than 1400MBps? (referencing the sequential read of the tested drive)
    SATA3 has a theoretical max of 6Gbps (750MBps). However, the practical max is more around 600MBps.
    Assuming you are running your Intel 730's in RAID-0 and achieving the max practical throughput, you'd still only come up with ~1200MBps which is slower than what Tom's saw at 1400MBps ON A SINGLE DRIVE.

    Quote:
    obamaliar, how do you reckon that your 740MBps or 948MBps is faster than 1400MBps? (referencing the sequential read of the tested drive)
    SATA3 has a theoretical max of 6Gbps (750MBps). However, the practical max is more around 600MBps.
    Assuming you are running your Intel 730's in RAID-0 and achieving the max practical throughput, you'd still only come up with ~1200MBps which is slower than what Tom's saw at 1400MBps ON A SINGLE DRIVE.
    Evolution 2001, I am referring to OS simulated performance IE CRYAN's PCMark 8 extended testing. Please read the article and you would understand that sequential performance is really a non-factor in comparison to random performance in an OS environment. Right now, SATA RAID has vastly superior random performance to PCIe drives like the X941, even if you were to soft RAID a pair of X941's together they cannot match a pair of good SATA SSD's in RAID in an OS environment. I cannot show you that exactly because Soft RAID is not bootable. look here: https://www.facebook.com/groups/1445011539065390/ there ia a pair of X941's soft raided getting their asses kicked by SATA RAID. The reason? 4K writes do not scale on PCIe drives. When PCIe drives can be RAIDed, bootable in RAID and have an RST type driver that allows for write caching Then they will become the superior OS disk.
  • 2 Hide
    cryan , June 10, 2014 11:57 AM
    Quote:
    Quote:
    obamaliar, how do you reckon that your 740MBps or 948MBps is faster than 1400MBps? (referencing the sequential read of the tested drive)
    SATA3 has a theoretical max of 6Gbps (750MBps). However, the practical max is more around 600MBps.
    Assuming you are running your Intel 730's in RAID-0 and achieving the max practical throughput, you'd still only come up with ~1200MBps which is slower than what Tom's saw at 1400MBps ON A SINGLE DRIVE.

    Quote:
    obamaliar, how do you reckon that your 740MBps or 948MBps is faster than 1400MBps? (referencing the sequential read of the tested drive)
    SATA3 has a theoretical max of 6Gbps (750MBps). However, the practical max is more around 600MBps.
    Assuming you are running your Intel 730's in RAID-0 and achieving the max practical throughput, you'd still only come up with ~1200MBps which is slower than what Tom's saw at 1400MBps ON A SINGLE DRIVE.
    Evolution 2001, I am referring to OS simulated performance IE CRYAN's PCMark 8 extended testing. Please read the article and you would understand that sequential performance is really a non-factor in comparison to random performance in an OS environment. Right now, SATA RAID has vastly superior random performance to PCIe drives like the X941, even if you were to soft RAID a pair of X941's together they cannot match a pair of good SATA SSD's in RAID in an OS environment. I cannot show you that exactly because Soft RAID is not bootable. look here: https://www.facebook.com/groups/1445011539065390/ there ia a pair of X941's soft raided getting their asses kicked by SATA RAID. The reason? 4K writes do not scale on PCIe drives. When PCIe drives can be RAIDed, bootable in RAID and have an RST type driver that allows for write caching Then they will become the superior OS disk.


    Actually, the 4 KB writes are really an artifact of the AHCI controller/API. If you took the same flash and controller on the Sammy, but rigged it to use NVMe, I think you'd see a big bump in random 4 KB performance. I've said over and over that desktop users, for now, are better off by using a couple SATA drives in RAID. More than just adding bandwidth, which isn't always important (strictly speaking), it lowers service times significantly. Plus, it's great to just keep adding cheap drives and getting more performance and capacity (when striped). See the Plextor M6e PCIe review for my thoughts on this.

    It's all academic anyway, since you can only buy the XP941 from a few random places, and it's $750. If I had a laptop which could use it, maybe I go that route, but even there SATA is just more power efficient. Give me a 1 TB EVO or M550 instead..... at least for the time being.

    PS: Is this Jon C??

    Regards,
    Christopher Ryan
  • 0 Hide
    obamaliar , June 10, 2014 1:24 PM
    Thanks for the reply love your stuff C Ryan :) 
  • 1 Hide
    Eggz , June 10, 2014 3:42 PM
    Quote:
    Give me [either a 750 GB] or a 1 TB EVO or M550 instead..... at least for the time being.


    Totally agree! For now.

    I also added the 750 EVO in there because (I believe) the only difference between the 1TB and the 750GB is capacity, unlike the smaller drives, which actually have less performance (i.e. 120, 250, & 500 GB).
  • 0 Hide
    logainofhades , June 27, 2014 11:59 AM
    I would rather use a single powerful GPU anyway, so the cut to 8x due to the ultra M.2 slot doesn't bother me at all. This is definitely and interesting board. I want an Ultra M.2 slot on a mini-itx board. :D 
  • 0 Hide
    lukebutters , July 15, 2014 7:32 PM
    If the RAID controller is set up with 4 disks in RAID 10, will the DMI limit be reached?