SSHD speed- NAND or RPM more important?

Discussion in 'Mac Pro' started by macmesser, Mar 23, 2016.

Tags:
  1. macmesser macrumors 6502a

    Joined:
    Aug 13, 2012
    Location:
    Long Island, NY USA
    #1
    I'm making an eSATA boot drive for my Macs using an OWC usb 3/eSATA III enclosure with a 2.5 inch form factor. Seems to be the only enclosure they have with both connectors, which I need since my Mac Mini does not have eSATA. The 2.5 inch size limits my choice of SSHDs to 5400rpm as far as I can find. Typically a 1TB (5400 rpm) SSHD has 8GB NAND.

    Will the slow rpm drive really perform close to SSD speed and is rpm not very significant in a hybrid drive? How much faster will a 7200rpm SSHD with 8GB NAND be than a 5400rpm with 8GB NAND when used as boot drives?

    Looking at it from amount of NAND perspective, at the same rpm would 32GB NAND be much better than 8GB for boot drive? Would a 5400rpm drive with 32GB NAND likely perform better or not as good as a 7200rpm drive with 8GB NAND?
     
  2. pastrychef macrumors 601

    pastrychef

    Joined:
    Sep 15, 2006
    Location:
    New York City, NY
    #2
    When I tested out one of these hybrid drives, I didn't find it anywhere near as fast as an SSD.
     
  3. AidenShaw macrumors P6

    AidenShaw

    Joined:
    Feb 8, 2003
    Location:
    The Peninsula
    #3
    Agree - they can be significantly faster than a spinner without NAND, but you'd have trouble coming up with a useful workload where they run in the SSD ballpark.

    One place that they can be a big win is with small random writes. This is because the Seagate SSHDs enable the writeback cache on the drive - so a burst of writes goes into the DRAM cache.

    Normally one wouldn't enable writeback caching, because a sudden shutdown could lose data and corrupt the filesystem. Seagate uses the NAND as a backup for the writeback cache - in the event of a power failure with dirty data in the cache the cache data is saved on NAND.

    Check out http://www.storagereview.com/seagate_laptop_sshd_1tb_review for in-depth reviews of many drives.
     
  4. macmesser thread starter macrumors 6502a

    Joined:
    Aug 13, 2012
    Location:
    Long Island, NY USA
    #4
    I'm seeing different results in product reviews. 73% 5 stars but even some of these report not as fast as SSD. I ordered a Seagate with 32GB flash for some extra cost. All of the reviews I saw were for the 8GB variant, so we'll see how 32GB works. A few negative reports about failure or weirdness of the 8GB model were a little scary but there were a low percentage of these.
    --- Post Merged, Mar 23, 2016 ---
    Thanks for comment and link. Will check. I typically am working with 10-25MB Photoshop files and small filemaker pro databases. The boot disk I am creating will allow me to run another legacy app that maxes out at OS 10.8.5 until I decide on replacement, plus maintenance utilities for my Macs. My Macs boot from SSDs on SATA II. The external boot drive will be connected via a decent eSATA (III) card so I'm hoping to get similar or better performance to when booting from the SSD.
     
  5. pastrychef macrumors 601

    pastrychef

    Joined:
    Sep 15, 2006
    Location:
    New York City, NY
    #5
    You will be much better off connecting your real SSD to eSATA and connecting the hybrid drive to the SATA 2. The hybrid drive will never come close to saturating the SATA 2 bandwidth while the SSD can make full use of SATA 3.
     
  6. orph macrumors 6502a

    Joined:
    Dec 12, 2005
    Location:
    UK
    #6
    depends what you want from the drive, if size is important to you then it's a lot cheaper to get a
    SSHD thats 1 TB than a 1 TB ssd.
    whats the currant drive, is it a SSD or HD? it might be important to you that the new drive feels faster.

    if your mac min has USB3 you might want to look at a small SSD for boot via esta (if it is just an boot drive something like 128GB/250GB might be ok and fairly cheep) then a USB3 HD for files.
    apart from that i think a SSHD will be faster than a normal HD & like a normal HD a 7200RPM drive is always faster.
    10-20mb Photoshop files are not that stressful on a system & if you are not low on ram your not going to need a fast drive. if you have 8GB or more ram you shude not have problems with Photoshop unless your working on a lot of images at the same time.
    i dont know what filemaker pro databases need to run, so some one will have to chime in on that.
     
  7. macmesser thread starter macrumors 6502a

    Joined:
    Aug 13, 2012
    Location:
    Long Island, NY USA
    #7
    Thanks. Hadn't thought about that at all. Question is, how much more bandwidth will an SSD saturate than the SSHD? They all appear to imply 6GBs throughput when you look at the specs. I did want a 1TB drive and I want to be able to boot from it for maintenance and to run an older OS to maintain compatibility while I do a data conversion/upgrade. In fact, I'll be needing two so the cost is a factor. I do hate buying less than optimal for what my setup will support so will do some shopping on SSDs. The one I bought has a 32GB SSD share and 1TB 5400 rpm HD. I thought the large amount of flash memory would mean it would perform much like an SSD. Will be testing soon.
    --- Post Merged, Apr 1, 2016 ---

    Thanks for reply. My macs do have usb3. Just upgraded. I do that on my Mac Pro. I have a 256GB SSD boot drive and a 128GB SSD scratch volume which work well with MP's SATA II controller. I have an eSata III card which I got for the Mac Pro. Maybe I'll use the SSHD for data and pick up a smaller SSD.
     
  8. pastrychef macrumors 601

    pastrychef

    Joined:
    Sep 15, 2006
    Location:
    New York City, NY
    #8
    Most modern SSDs can do about 500-550MB/s reads and writes. This would match well with SATA 3's theoretical limit of 600MB/s. Since any drive not connected to the built-in SATA connectors of the Mac Pros 1,1-5,1 will appear as external anyway, it really makes no difference if you use eSATA.

    I'm also interested in seeing what type of performance you will get from your SSHD. The one I tested with only 8GB NAND performed no better than a quick traditional 7200RPM 3.5" drive. Connecting it to SATA 3 was just waste of time.
     
  9. AidenShaw, Apr 2, 2016
    Last edited: Apr 2, 2016

    AidenShaw macrumors P6

    AidenShaw

    Joined:
    Feb 8, 2003
    Location:
    The Peninsula
    #9
    Three things....
    1. SSHDs "learn" what your usage patterns are, and migrate frequently read items into the cache. When new, the cache is empty and you see the performance of a spinner.
    2. Synthetic benchmarks often read and write huge files, which again effectively flush the SSD cache by having no reuse of blocks.
    3. The Seagate SSHDs unconditionally enable the on-disk DRAM cache in write-back mode, so that writes are "completed" almost immediately from the viewpoint of the OS. This greatly speeds up operations that create or modify lots of smaller files (like temp files), since writes happen at SATA bus speed and no head movement latencies are seen.
    In other words, the SSHD can make Safari and other apps feel "snappier" - even if synthetic disk benchmarks don't show that.
     
  10. deconstruct60 macrumors 604

    Joined:
    Mar 10, 2009
    #10
    Not much. What you have is the same size "fast cache". The size of the cache is what is making the difference. Should be concerned about the ratio of the NAND cache to the capacity of the spinning portion of the drive. 8GB of 500GB drive is 1.6%. That is pretty small. 8GB of 1,000GB (1TB ) is 0.8% which is definitely small. Rounded down to the nearest integer that is zero. 8GB of 2TB is an even close approximation of zero.

    What the cache is going to do is move your "hot spot" data into the NAND. The essential core of your OS and perhaps 1-2 apps can be moved into 8GB. You will get faster than a HDD performance overall and around the same speed as a SSD for that narrow, often used, subset. You boot and app lauches will be faster. Some of your most used App usage will be faster.


    Not necessarily going to speed up boot much. The vast bulk of an OS resting footprint size is not the same as what is needed to boot/load. ( almost always going to have drivers/resources for stuff you don't have plugged in at boot. ) 32GB is ~6% of 500GB. Still in the sub 10% coverage range for the cache.
    ( if the NAND cache controller can shift between MLC and SLC then a "thinned out" (i.e. SLC mode) so had pragmatically 8GB of MLC and 8GB of SLC. That would might help. I don't think any of the current hybird are up to that level of sophistication yet. ). With a decent amount of SLC might get incrementally more write caching being done.
     
  11. orph macrumors 6502a

    Joined:
    Dec 12, 2005
    Location:
    UK
    #11
    boot times never bothered me much, booting from WD blacks HD's are fairly fast and i only boot once every few days normally so :V shore all the boot stuff was just to sell SSD's
    (turn of auto power down of HD's in system preffs helps if you want a tad more responsiveness when working with a few dries in your mac)
     
  12. macmesser, Apr 4, 2016
    Last edited: Apr 4, 2016

    macmesser thread starter macrumors 6502a

    Joined:
    Aug 13, 2012
    Location:
    Long Island, NY USA
    #12
    Current boot drive is a 240GB Mercury Extreme Pro ssd from OWC. The new drive will be an esata boot drive. I hope the 32GB flash and faster SATA III will somewhat offset the 5400 rpm. I think it will be OK as it will be used for a data conversion which forces me to stay at OS 8.5 to run a necessary program. Mostly smaller files. Will also have maintenance and diagnostic tools.
    --- Post Merged, Apr 4, 2016 ---
    I'll post results. Was going to set the drive up tonight until I realized that I need a power adapter for eSATA. (Using an OWC Elite Pro Mini 2.5 enclosure with eSATA and USB 3. Since it won't boot in USB 3 I'm waiting for the adapter.) If I get at least your results with 8GB my 32GB SSHD should perform somewhat to significantly better than a 7200rpm spinner. Considering that it will be on SATA III, good enough for my purposes.
    --- Post Merged, Apr 4, 2016 ---
    So my 32GB fast cache is around 3.2% of the 1TB capacity. I can see how this % is an index of the performance boost but it seems that if you go past a certain point it would diminish in importance. It also seems that as fast cache got bigger the capacity of drive would diminish in importance as well. Unless I'm missing something, which I might well be.
     
  13. macmesser thread starter macrumors 6502a

    Joined:
    Aug 13, 2012
    Location:
    Long Island, NY USA
    #13
    Thanks. This didn't ring a bell when I first read it but it just dawned on me that I could do this quite conveniently. I can create a 240GB boot partition on the SSHD and clone my SSD boot drive, then swap out the old boot drive for the partitioned SSHD. I could then use the SSD in the enclosure either as boot drive or for maintenance and the Mac Pro would have an extra bootable partition which would probably be close in performance to the SSD on the SATA II bus.
     
  14. orph macrumors 6502a

    Joined:
    Dec 12, 2005
    Location:
    UK
    #14
    you can also just install the new drive, install osx then plug in the old drive and tell osx to migrate the user over, no need to partition unless you want to.
    you can migrate over during the osx install process or via migration assistant app in the utility's folder after you have installed osx.
    you cant migrate to a older version of osx but you can to a newer version.

    you can even if the external drive is bootable (can you boot from an external esta drive? you can boot from a usb/firewire drive) boot from the external drive install osx from the external drive on to the new internal drive either from the recovery partition or the installer in the app folder tho if the recovery partition is booting via the internet it will be slower.
    then boot in to the internal drive and migrate the user form the old drive.
    (to migrate a user over from the external drive dose not need to be bootable)

    i think even if you clone you dont need to have matching partitions if you do opt to clone the drive (not 100% shore on that tho)

    there is nothing wrong with having 1 partition for osx and apps and one for data & you can have things like itunes/photos data folder on the data partition instead of the osx partition if you want.

    no HD will max out SATA 2 or 3 speed (unless in raid with a bunch of drives) and only the SSD catch on a SSHD will potentially max out the SATA 2 speed but your not going to see a massive change from SATA 2 - 3 for normal use.

    The SSHD will be slower than an SSD but i never had a real problem with booting and using WD black drives for general computer use and as i mentioned boot time is not a big thing, turn of auto drive sleep in the system prefs energy saver section will help a HD be more responsive.
     

Share This Page