More/Better Internal Storage on the Toshiba AC100

One of the unfortunate things about the AC100 is that the internal storage isn’t removable, and thus isn’t easily upgradable or replaceable. The latter could be an issue in the longer term because it is flash memory, so it will eventually wear out, and I since it is relatively basic eMMC, I don’t expect the flash controller to be particularly advanced when it comes to wear leveling and minimizing write amplification. Using the SD slot is an option, but if we are running the operating system from it, we cannot use it for removable media, which could be handy. We could use a USB stick instead, but then we lose the only USB port on the machine. There is no SATA controller inside the AC100.

What can be done about this? Well, models that have a 3G modem have it on a mini-PCIe USB card. Even though Tegra 2 has a PCIe controller built into it, the mini-PCIe slot isn’t fully wired up – only USB lines are connected. Since most of us can tether a data connection via our phones, and since this is more cost effective than paying for two separate mobile connections, the 3G module isn’t particularly vital. The main issue that the slot only has USB wired up. So what we would need is a USB mini-PCIe SSD. Is there such a thing? It turns out that there is. I have been able to find two:

  1. EMPhase Mini PCIe USB S1 SSD
  2. InnoDisk miniDOM-U SSD

The specification of the two modules is virtually identical (both use SLC flash among other similarities), so I decided to investigate both of them. Unfortunately, having contacted an EMPhase re-seller, they called me back having spoken to the manufacturer and talked me out of buying one, citing unspecified issues.

My local InnoDisk re-seller was more interested in selling me a product, but there were two reasons why despite very good pre-sales service I ultimately decided against buying one of these. The first and foremost was the performance specification. According to the manufacturer’s own figures, the random access performance with 4KB blocks is 1440 random read IOPS and 30 random write IOPS. Considering the price per GB of these modules is approximately 4x that of similarly performing SLC SD cards, this module was discarded on the basis of cost effectiveness.

Having discarded the above modules, there are still a few alternative options available. The low risk, tidy options include an SD mini-PCIe USB adapter and a micro-SD mini-PCIe USB adapter. They are very reasonably priced so I got one of each for testing, and I am pleased to say that they work absolutely fine in the AC100. Here is what they look like fitted into the AC100.

Dual micro-SD mini-PCIe USB Adapter
Dual micro-SD mini-PCIe USB Adapter
SD mini-PCIe USB Adapter
SD mini-PCIe USB Adapter

The SD cards will appear as USB disks. If you use the dual micro-SD adapter you can RAID the two cards together.

Unfortunately, I have found that the best results are achieved using a single SD card, purely because I haven’t found any micro-SD cards that have reasonable performance when it comes to random-write IOPS. SD cards fare a little better, but the best SD card I have found in terms of random write IOPS still tops out at a mere 19 random write IOPS using 4KB blocks. Still, it is 2/3 of the marketed figures for the InnoDisk SSD at 4x lower price per GB, and the performance just about scrapes past what I would consider minimal requirements for reasonable use.

I am currently putting together a list of SD, micro SD and USB flash devices and consistent benchmark performance figures for them, which should hopefully help you to choose the ones most suitable for your application. I hope to have the article up reasonably soon, but don’t expect it too soon – benchmarking SD cards takes a long time to do properly.

6 thoughts on “More/Better Internal Storage on the Toshiba AC100

  1. well.. with better screen, shims for cooling and therefore overclocking and this.. how much would you guess a really expensive and maxed-out AC100 now? I mean including work-hours?

    I still have hope left, for someone going to built something armada15000- or tegra3-based in the comming year. I know it isn’t really likely, but the probability exists nonetheless.

    • Well, if you know exactly what you are doing (i.e. you have either done it before, or are following my instructions), you could probably get the full upgrade completed in under an hour. How much that is worth depends on three things:
      1) What you think your time is worth
      2) Whether you are doing it for fun
      3) Is there a viable alternative that provides the same features without modifications

      But at least the parts are easy to price up – and with all the parts it’s still cheaper to get an AC100 and modify it than it is to get a Transformer. Then again, I’ll likely modify that, too, when I get one. In fact, it’s cheaper even if you account for an hour of labour to mod it at any realistic hourly rate.

    • Indeed I will include it. I already measured it and as far as performance is concerned the internal storage is actually very good.

    • Of course it is. You can boot Linux from any device your kernel knows how to access. The SD Card in the PCIe slot shows up as a USB disk. The device in the slot is a normal USB card reader.

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