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Thread: Hybrid Drive - Doesn't support Trim?

  1. #21
    Jazz
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    Angry Official...

    The drive used in the T100TA is NOT an SSD drive, it is a multimedia card which is soldered onto the motherboard... The reply which I received from CS...

    Yes, the T100TA uses an embedded Multimedia Card, this is the common technology for mobile devices just like the T100TA. The fash memory is soldered to the motherboard. SSD is commonly use on desktop or laptop where the SSD is connected to a socket and uses SATA host interface.
    Which reduces the expected life expectancy considerably

  2. #22
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    Quote Originally Posted by i2McAbre View Post
    The drive used in the T100TA is NOT an SSD drive, it is a multimedia card which is soldered onto the motherboard... The reply which I received from CS...



    Which reduces the expected life expectancy considerably
    Well, yes and no. Yes it is probably somewhat lower life exptancy, but depending on what kind of eMMC it is, it often has most/all of the features of a full fledged SSD. Technically an eMMC IS a Solid State Drive. It is just that SSDs commonly have controllers that have 6-10 "channels" with each channel populated by 1 or more NAND flash chips. eMMCs typically are single channel controllers, controling 1 or more NAND flash chip. Much more compact design, lower power consumption, cheaper and of course lower performance, because you have 1/6-1/10th the possible parrallelism that a full fledged SSD has. There may be some dual channel eMMC controllers, but I am not aware of any.

    As an example of decent, if not great, performance, the Sandisk 64GB eMMC module in my T100 seems to hit around 114MB/sec reads and 42MB/sec writes under ideal work loads. With 4k random I/O it hits around 20MB/sec reads and writes (about 5000 IOPS), which actually ain't terrible. The 4 year old 60GB OCZ Vertex I have is not a lot faster for 4k performance, it only hits about 28MB/sec writes and 35MB/sec reads for 4k performance (about 7000/12000 IOPS), though its sequential performance is a lot better at around 210MB/sec reads and 130MB/sec writes.

    There are obviously eMMC solutions that are much worse.

    Also some don't implement things like TRIM. The Sandisk eMMC module DOES implement TRIM. It looks like the Hynix model does not implement TRIM.

    For life expectancy, most current SSDs have between 3,000-5,000 Program Erase cycles for endurance (MLC drives). I have no clue on the endurance, and I notice in the specs there is says TBD, which isn't exactly encouraging. It might also be TLC based, which means worse endurance and performance.

    The Sandisk eMMC modules in the earlier T100s (32 and 64GB) have a rated endurance of 3,000 P/E cycles IIRC from the spec sheet, or something there abouts.

    How any given controller handles garbage clean up, writes, TRIM, etc varies. It is something called write amplification and also depends on the work load. Generally small file writes increase amplification significantly as SSDs have something called a page and block size. They can only write to a page as whole. So if you have a 64 kilobit page size, if the OS wants to write a 3 kilobit file to storage, depending on how the contrller handles it handles it, it is going to write 3kb in to an entire page and the rest will be empty. If space fills up, later on a new write comes in and there are new unwritten pages, but there is free space in the page, the NAND flash controller will read out the page to the controllers memory, erase the page (set it all to zeros), and then it'll write back out both the old data and the new data to the page.

    So you can see how this can cause issues, especially with small files, and this is part of garbage collection. The controller will periodically go through and consolidate pages when its idle, so that when the OS wants to write something, there will be empty pages where the controller can just write directly to a free page, instead of having to erase it, which takes SIGNIFICANT time, and then write to it once it is erased. So you have the initial write to the page, then you have garbage collection erasing the page later for consolidation, and possibly writing the data back in to that page or another one, along with some other data. Then you might have the controller erasing and writing data in to the page again even later with more garbage collection if the page hadn't been filled, or there are no free pages and the current page has some free space unutilized still.

    Anyway, that is the amplification bit. A good controller with resonably large files, say, MP3s, movies, images, maybe PDFs and word documents and stuff, can fill one or more pages (or thousands of pages) with a single file and tuck it all in neatly. Assuming garbage collection and TRIM have been doing their job, you'll have lots of empty pages, unless your NAND flash is close to full (TRIM is garbage collection, enforced. It tells the controller, all deleted data, erase and consolidate those cells. Now. Garbage collection will often do the same thing, but it is wholely controller dependent and can take hours, days or never to clean up pages with deleted data in it. So you might have a page with zero data that the OS and controller care about, but still has 1's written to it, because the controller never did garbage collection on it and the controller doesn't obey TRIM commands to trim up the deleted data).

    So, anyway, big files typically see a write amplification of between 1.3-2.0 with a good controller. That means for every 1GB of data written, 1.3-2.0GB of the flash storage will have undergone a P/E cycle (either immediately, or over a period of minutes/hours/days after the write due to garbage collection and TRIM). Small files, like sustained 4k writes can see write amplifications of 5-8x with a good controller, and some of the really crap ones are in the 10-20x range with 4k (or even smaller) writes. Most files though are not 4k in size. Most are resonably large in scoop, such that write amplification is probably in the 2-3x range on average.

    With a 3k P/E endurance eMMC module or SSD, at say 64GB in capacity, lets say 50GB user capacity and 20GB of that more or less permenantly inhabited by the operating system, which is going to be static and not move around, that is about 30GB that can/will be written to over time (unless you leave it full most of the time), that gives you about 30TB worth of writes to the eMMC module if you experience 3x amplification. Most workloads for a solid day of use (don't forget things like page file, hibernation file, applications writing things, etc. It isn't just loading and deleting things conciously as the user) is in the 5-15GB range. Which means 5-15 years worth of endurnace probably.

    Even if it is a crappy controller with high write amplification, that is maybe 2-6 years of endurance. Of course if you keep very little free space, oh like say the 32GB model, which can only have around 10GB free, it might be more like 2-6 years with a good controller.

    Since this is a tablet, assuming lighter workloads, for the 32GB model, probably 4-7 years is my personal guess. Unless you leave the thing really filled to the gills most of the time with very little free space, then you might wear out what space you are doing the writes to in only a year or two, but probably unlikely.

 

 
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