Using the BBGW MicroSD card for direct-access emulation files

[Forgotten Machines]

Since Decromancer.ooo is now reselling this emulator, they are providing this letter of instructions when they ship it:

https://decromancer.ooo/mfm-emulator/Pack_In_Letter_Rev5.pdf

They are shipping it with the BeagleBone Green Wireless (BBGW), which I have never used.  My experience is exclusively with the Beaglebone Black and BeagleBone Green with Ethernet.

Please note the section that says " The MFM Emulator now ships with a free 4GB microSD card. This card is mounted by default at /mnt. We recommend placing any drive images you wish to emulate on this card, to prevent eMMC wearout."

Now, maybe I'm just operating from older information, but I seem to recall a strong warning from David G. about NOT using the MicroSD card to directly access the emulator files when emulating a hard drive, but rather always copy emulator files to the onboard eMMC and run emulators from that location exclusively.  This is what I have always done, and it has always worked for me.

Was the reason for this that back in 2015 when I started using these devices, that general use MicroSD cards were not fast enough to support the read/write time needed for hard drive emulation?  OR was it that the older hardware BBB couldn't read/write to the SD card fast enough?  Or another reason?

And could it really be OK now with the BBGW to read emulator files direction from the MicroSD?

I appreciate anyone's feedback on this, and thank you.

Best,

AJ

[David Gesswein]

On Fri, Apr 08, 2022 at 01:46:27PM -0700, Forgotten Machines wrote:
>
> Please note the section that says " The MFM Emulator now ships with a free

> 4GB microSD card. This card is mounted by default at /mnt. *We recommend

> placing any drive images you wish to emulate on this card, to prevent eMMC

> wearout.*"

>
> Now, maybe I'm just operating from older information, but I seem to recall
> a strong warning from David G. about NOT using the MicroSD card to directly
> access the emulator files when emulating a hard drive, but rather always
> copy emulator files to the onboard eMMC and run emulators from that
> location exclusively. This is what I have always done, and it has always
> worked for me.
>

I don't really know what I've said on this. Their are high endurance uSD
cards that likely will have better life than the eMMC. Suspect cheapest card
will be worse but no real data. Likely can get higher performance cards than
the eMMC.

For the usage most machines get it probably doesn't matter. Don't think
people are doing heavy writes 24 hours per day with my emulator. I have not
had any reports of eMMC issues.

> Was the reason for this that back in 2015 when I started using these
> devices, that general use MicroSD cards were not fast enough to support the
> read/write time needed for hard drive emulation? OR was it that the older
> hardware BBB couldn't read/write to the SD card fast enough? Or another
> reason?
>

eMMC was there so why have people go to the trouble of setting up a uSD
card. If you do wear out the eMMC you can just boot the board off the uSD so
you don't have to toss the board. In 2015 a number of cards had abysmal
random write performance. Probably some still around.

[Joan Touzet]

Hi AJ, David:

On Friday, April 8, 2022 at 6:45:49 p.m. UTC-4 d...@pdp8online.com wrote:

On Fri, Apr 08, 2022 at 01:46:27PM -0700, Forgotten Machines wrote:
>
> Please note the section that says " The MFM Emulator now ships with a free
> 4GB microSD card. This card is mounted by default at /mnt. *We recommend
> placing any drive images you wish to emulate on this card, to prevent eMMC
> wearout.*"
>
> Now, maybe I'm just operating from older information, but I seem to recall
> a strong warning from David G. about NOT using the MicroSD card to directly
> access the emulator files when emulating a hard drive, but rather always
> copy emulator files to the onboard eMMC and run emulators from that
> location exclusively. This is what I have always done, and it has always
> worked for me.
>

I don't really know what I've said on this. Their are high endurance uSD
cards that likely will have better life than the eMMC. Suspect cheapest card
will be worse but no real data. Likely can get higher performance cards than
the eMMC.

For the usage most machines get it probably doesn't matter. Don't think
people are doing heavy writes 24 hours per day with my emulator. I have not
had any reports of eMMC issues.

 

The warning is perhaps a bit strongly worded. The issue is that if you wear out the eMMC, you can't replace it - but you can replace a microSD card. We did have a customer wear their eMMC out with heavy writing (they were using the BB for more than just drive emulation), and they were surprised that this couldn't be directly addressed aside from replacing the entire (expensive) BeagleBone - or using alternative storage means (as David mentions below).

I believe the eMMC on the BeagleBone is MLC NAND based, which is approximately 10k write cycles per block - relatively low. (reference: https://groups.google.com/g/beagleboard/c/w2cApA3ed4A )  In addition, the more free space you have, the more wear-leveling the flash controller can provide - so, placing emulated drive images on separate, mostly blank media can further extend flash lifetime.

If people are really concerned about extra-long durability, future work might consider mounting the root partition read-only from eMMC, and even considering moving /var to a  tmpfs instead of writing-through to the eMMC at all.

> Was the reason for this that back in 2015 when I started using these
> devices, that general use MicroSD cards were not fast enough to support the
> read/write time needed for hard drive emulation? OR was it that the older
> hardware BBB couldn't read/write to the SD card fast enough? Or another
> reason?
>
eMMC was there so why have people go to the trouble of setting up a uSD
card. If you do wear out the eMMC you can just boot the board off the uSD so
you don't have to toss the board. In 2015 a number of cards had abysmal
random write performance. Probably some still around.

Of course this is also possible - but you're down to a single file system this way, unless you add a USB thumb drive. It's just nice to be able to boot off of the internal eMMC, and have (one or more) drive images on the microSD. Aside from system logs, this keeps eMMC writes to a minimum.

Many different approaches exist. Put three engineers in a room and get six opinions out of them :)

-Joan

 

[Forgotten Machines]

Thank you both, David & Joan for clarifying your thoughts on this.  It helps me put it into prospective.  So then, a proper command line for starting an emulated drive on the decromancer.ooo configured auto-mounted MicroSD card would look like this?

./mfm_emu -d 1 -f /mnt/NGEN-c820h6.emu

Correct?

[Joan Touzet]

Looks good.

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