Primary drive: Dual SD cards in RAID 0

This is an idea for the next generation of Librem 5 phone.

Make the primary drive two SD cards that can be configured in RAID 0.


  • Personally upgradable
  • Quickly swap OS via hardware without having to redo installations
  • Choose between 1 and 2 SD cards
  • Faster read/write speeds

hello ! if this is a joke then i’ll smile :slight_smile: but in case it isn’t then:

sd cards are horribly slow not only by themselves in any kind of raid as well. they simply are not made for such purposes.

what makes a good bootable ssd is not only sequential read/write speed but also the latency.

for example in terms of latency sd<HDD<SSD(sata)<SSD(nvme)<the next best thing :wink:

you can put 10 sd in raid and it would not touch a HDD.

why not buy an external HDD/SSD SATA III external docking module that connects to the pc with a usb 3.0 (male type A - use a separate adapter to usb c ) and try that on the librem 5 (v1 or later) ? that’s just for static/indoor use ONLY …

I didn’t realize the phones used ssd. I really thought they used something practically like flash anyway.

The performance can’t be that bad especially when you get nicer sd cards. I certainly would not want to have to attach external drives to my phone.

Check out microSD Express. Hopefully something like that will be established by the time they get to making a 2nd generation Librem 5. You know how that stuff keeps getting faster all the time.

Unfortunately I couldn’t find any data on the storage they are using. Anyway consider the idea of removable storage as a thinker. Hard to argue with the coolness and freedom of that.

UFS 3.0 and microSD Express cards

They say UFS itself could make its way into SD cards. (Although something tells me that Purism might not be able to single handedly make that come to pass. You never know.)

My guess is that manufacturers do not want removable storage enough to make it happen. They do not want people having phones that are just as configurable as desktops. . . chaos.

Consider two microSD Express cards in RAID 0. Might even be faster than UFS 3.0. It would almost certainly be faster than the current UFS. Now consider you might not need bleeding edge, but openness.

I don’t know that RAID 0 is that big a deal when the next generation design can just get a faster SD card / reader, and, as you commented already, there isn’t any info about what the spec of the SD card reader is currently for the Librem 5.

One concern about SD cards is how reliable they are. It is all very well for them to be high capacity and fast but if they are not reliable, I won’t want it. So it needs to be a quality card. By suggesting RAID 0, you are making this problem worse.

An alternative approach, for a future version of the phone, would be to keep the existing eMMC drive but allow you to swap the roles of the two drives i.e. boot from SD card and use the eMMC drive as additional storage. Whether that fully makes sense depends in part on what capacity SD card you plan to use. That only addresses one of your bullet points however.

It is possible that this could partly be achieved by using a chain boot, which may avoid the need for any code changes to the “BIOS”. (This is the reverse scenario to the Raspberry Pi, where it wants to boot from SD card by default but some people may attach additional storage and really want to boot from that.)


May be ditch the baseband AND INSTALL A 1TB M.2 CARD !!!

How would it still be a mobile phone?

It it doubtful that doing that would work with the current phone. A slot for an M.2 modem card may well be incompatible with a slot for an M.2 disk card (NVMe or SATA). They may be physically incompatible (due to how they are keyed). Even if physically compatible (keyed compatibly, can physically insert in slot), may not be electrically compatible i.e. using different pins for different purposes.

However … since the original comment was about the “next generation” it could be doable, theoretically.

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Ohhh , I was wondering if those M.2 were proprietary to the baseband or whether they worked with other M.2 devices.

I was half jokin . I guess easily removeable base band you could swap it out when you needed a phone. The wifi would still work lol .

theres probably no room for a 1tb M.2 anyways .

Also true.

The BM818 modem says that it’s 30mm wide and 42mm long, whereas the NVMe drives that I have are 22mm wide and 80mm long. There are a bunch of valid form factors defined by the M.2 spec and both of those are valid but it does mean that you can’t just unplug and plug - and as you say in this particular application, the card might not fit in the phone anyway.

If you have booted from the M.2 disk then you will need an operating system variant that can be memory resident (which is not too demanding). You would also need to be careful with how any applications behave when the disk that contains files that they are accessing goes away temporarily while you make a voice call or access the internet via a data call. ???

One concern about SD cards is how reliable they are. It is all very well for them to be high capacity and fast but if they are not reliable, I won’t want it. So it needs to be a quality card. By suggesting RAID 0, you are making this problem worse.

This, precisely.

Visit any photography forum and you will run into people who (for example) shoot weddings and insist that their work camera must have TWO card slots. Because they fear getting sued if one card craps out and takes their clients’ pictures down the drain. They set the camera up to save everything to both cards (sort of as if it were RAID 1).

Running something as unreliable as an SD card in RAID 0 (striped) so that either card going down destroys everything…would scare the crap out of me.


Or the wedding photographer uses a camera with built-in WiFi and it backs up in real-time to a nearby other device e.g. the photographer’s phone. Yeah we’re talking a fairly sophisticated camera. :slight_smile:

In the context of the Librem 5 by itself creating files that is probably doable. Could be a nice little appliance for Purism to make and sell - or backup to internet. But I still wouldn’t jump at the chance to have either only a single SD card (no eMMC) or a RAID 0 pair of SD cards.

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Some cameras let you do that (though throughput would have to be very high), but I brought it up to make the point that SD cards are not considered very reliable. Putting them in a Raid 0 would scare the heck out of me…and IIRC you’d basically agree.


for an internal m2 ssd in a L5 as nvme bootable storage (if that’s ever a thing) you’d also (probably) not like the heat dissipation either making your hands cook more …


Perhaps M.2 SATA SSD runs cooler since it runs slower.

I’m not hanging on to replace my M.2 modem with M.2 storage anyway since I would like to use my mobile phone as a, you know, mobile phone.

Within the constraints of not wanting to have untrusted devices with direct access to memory, you probably don’t want any stock M.2 storage device. You would need a cross between a stock M.2 SSD storage device and an external portable SSD with USB interface. (That would then be too slow to contemplate using an NVMe-capable SSD device.)


The last few paragraphs of this pdf sum it up nicely, and go with what y’all are saying. Thanks.

Here’s a link for SD Express controller from Phison.

These comments still relate to older technologies, and may not apply to SD Express. (Though admittedly one initial appeal of the idea was the cost saving possibilities.)

If the newer SD technologies are indeed reliable enough, then the costs of implementing them may still be too high, because they are new technologies. And weighing in the chaos of having people buy unreliable cards does cause problems.

But still, the prospect seems like it still might be viable if these controllers and cards do indeed turn out to perform reliably, and the costs are not too high.

People would simply have to understand the risks they are taking by implementing such solutions, just as they would for the PC. Perhaps in this case, it would not be wise to include an ultra-convenient gui for such a thing unless the gui could also warn against the risks of using older SD technologies.

Even still, the interface could easily give warnings, and a readout of whether or not the SD card was an SD
Express or not.

You also need to take into account manufacturing economies of scale. Already we are looking (in this topic) at a bunch of different internal storage configurations:

  • eMMC + SD (what we will actually get)
  • 1 x SD
  • 2 x SD

Is there enough total demand / demand for individual configs to justify offering variations?