SG-2440 eMMC Questions / Concerns



  • Hello,

    I have a question regarding using eMMC in the SG-2440 with a "full" pfSense install.

    By default, the SG-2440 comes configured with the "full install". I am running the latest "Stable" version of pfSense 2.3_1 memstick installer.

    Everything is working great… I am running light traffic with snort and pfBlockerNG enabled.

    My concern is, does eMMC have the same wearing issues as an SSD drive – should I be concerned with the heavier data writing with snort, pfBlockerNG, and the logging that goes with all of this? Should I be concerned with the eMMC on the system board wearing out quickly? With this type of configuration, would installing an mSATA 30GB disk be advisable?

    Thank you for any advice and suggestions you can send my way,
    -Matt


  • Netgate

    Depending on when you purchased your SG-2440, you either have a Toshiba 4GB eMMC or a Kingston 8GB eMMC.

    You've probably noticed that pfSense isn't anywhere near the capacity of either of these.  there are reasons we didn't use a
    smaller eMMC, and they are not related to cost.

    I have an older 4860 at home, it identifies as:

    da0: 3648MB (7471104 512 byte sectors)

    A stock install will use approximately 2,000,000 sectors (mine at home currently uses 2,067,488m, leaving something over 5 million sectors free.

    For Multi-Level Cell (MLC) Flash, up to 3000 write cycles (this is the JEDEC minimum, many vendors claim higher figures) per physical sector based on current lithography process (19nm and 20nm) at the time of this writing.

    Enter wear-leveling.

    Flash memory media (and EEPROM) have individually erasable segments, each of which can be put through a limited number of erase cycles before becoming unreliable. This is. as above. usually around 3,000/5,000 cycles] but many flash devices have one block with a specially extended life of 100,000+ cycles that can be used by the Flash memory controller to track wear and movement of data across segments.  [https://www.researchgate.net/publication/277637285_A_Survey_of_Software_Techniques_for_Using_Non-Volatile_Memories_for_Storage_and_Main_Memory_Systems]

    Wear leveling attempts to work around these limitations by arranging data so that erasures and re-writes are distributed evenly across the medium. In this way, no single erase block prematurely fails due to a high concentration of write cycles.

    To put a point on all the above, by vastly over-provisioning the eMMC, more 'space' is available for wear-leveling, and the eMMC will last longer.  We put several in a torture test when we were fixing the UFS problems, and the eMMC stood up to the abuse much longer than any SDHC/SDHX/CF/microSD card we tested.

    You didn't ask it, but this is a fine time to talk about why we use eMMC rather than one of the SDHX card formats.

    Some SD cards use wear leveling, and some wear-leveling algorithms are designed for the access patterns typical of FAT12, FAT16 or FAT32.[http://lwn.net/Articles/428584/]. Since the wear-leveling is on the card, you don't know, and you can't control it.  In addition, SD cards come pre-formatted, and the preformatted file system may use a cluster size that matches the erase region of the physical memory on the card; reformatting may change the cluster size and make writes less efficient.

    SD/SDHC/SDXC memory cards have a "Protected Area" on the card for the SD standard's security function; a standard formatter may erase it, causing problems if security is used. The SD Association provides freely-downloadable SD Formatter software to overcome these problems for Windows and Mac OS X.[https://www.sdcard.org/downloads/formatter_4/index.html] The SD Formatter does not format the "Protected Area", and the Association recommends the use of appropriate application software or SD-compatible device that provides SD security function to format the "Protected Area" in the memory card.

    The SDXC specification (required for cards > 32GB) mandates the use of Microsoft's proprietary exFAT file system.

    Knowing all the above, guess what happens when you combine a wear-leveling algorithm which assumes FAT or exFAT with UFS.

    Yeah.

    In specific answer to your questions:

    does eMMC have the same wearing issues as an SSD drive

    they are similar, but not identical.

    should I be concerned with the heavier data writing with snort, pfBlockerNG, and the logging that goes with all of this?

    Possibly.  Have you measured it?

    Should I be concerned with the eMMC on the system board wearing out quickly?
    this is difficult to answer without knowing how much you're writing (say, per day).

    With this type of configuration, would installing an mSATA 30GB disk be advisable?

    Many people do this, and it is likely to result in fewer headaches and higher performance.

    What's it worth to you?



  • :) Wow!  :)

    Thank you so much for all of your insights and information. It sounds like an mSATA drive would be just the thing.

    Would this be a good one?? http://amzn.com/B00COFMPAM

    Do you know if opening the box to install the mSATA drive voids the warranty for the appliance?

    -Matt


  • Netgate

    Sorry, I don't recommend things that we don't sell.

    Yes, you void the warranty if you open up the system.



  • That's good to know. Thanks again for the added info! :)



  • @matthewdeets:

    That's good to know. Thanks again for the added info! :)

    By rule of thumb;
    16 GB firewall only
    30 GB Snort & pfBlockerNG
    60 GB Squid & Snort & pfBlockerNG
    120 GB Squid (caching proxy) & Snort & pfBlockerNG
    more GB = more users, more traffic and more cached objects


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