Did you know there's a whole raft of not-quite-genuine SD cards on the market? I only found out recently after buying some by accident.
Problems on eBay
As regular readers will likely know, my starting position when looking to purchase almost anything is to head to eBay. Planning to revive my RaspberryPi to run PiHole, I needed a new SD card.
eBay is awash with SD cards for sale. Lots of these are from ‘reputable’ sellers and at prices that seem very good. I purchased a few Lenovo cards and eagerly waited for them to arrive in the post.
Initial impressions were not great. The packaging is definitely not what I expected:
A genuine SD card or fake?
The packaging isn’t branded as Lenovo, actually it has zero mentions of Lenovo which seems unexpected. The micro SD card itself actually looks fairly legit. More investigation required.
Wondering if my worries were founded or not I tried to Google for Lenovo cards to see what the retail packaging should look like. I struggled to find any concrete information; others seem to be in the same boat.
Checking SD Cards with f3 - Fight Flash Fraud
f3 (Fight Flash Fraud), is a tool that checks the speed and capacity of your SD card is what you expect. h2testw is another such tool that gets a lot of mentions, but it’s Windows only.
I installed f3 on my mac using brew install f3, then started the write command against
the 256GB ‘Lenovo’ card.
➜ /opt/homebrew/Cellar/f3/8.0/bin/f3write /Volumes/NO\ NAME F3 write 8.0 Copyright (C) 2010 Digirati Internet LTDA. This is free software; see the source for copying conditions. Free space: 238.21 GB Creating file 1.h2w ... OK! Creating file 2.h2w ... OK! Creating file 3.h2w ... OK! Creating file 4.h2w ... OK! Creating file 5.h2w ... OK! Creating file 6.h2w ... OK! Creating file 7.h2w ... 0.03% -- 7.41 MB/s
It started just over 10MB/s but gradually slowed down to around 7.41 MB/s, much slower than I expected. Some highlights from the eBay ad…
- "TRANSFER SPEEDS OF UP TO 120MB/S"
- "LOAD APPS FASTER WITH A2-RATED PERFORMANCE."
- "Class 10 speed rating allows you to shoot Full HD video and high quality photos."
Class 10 cards are capable of at least 10 MB/s. We’re not reliably seeing that, let alone the ‘up to 120 MB/s’ claim. Note that the A2 rating doesn’t mean it’s any quicker than 10MB/s sequentially, just that the random read/write rate of IOPS meets a certain standard.
I decided to leave f3 to run over night (the estimated time to complete was
circa 5 hours). In the morning I’d then run the f3read utility to see if at
least the read speed was decent.
Fast forward to the next day, the program only got as far as 192GB of files before it exited. The SD card had failed, the laptop wouldn’t even recognise a card had been inserted and other devices I tried had the same result.
Buying Real Cards
Was that a ‘fake’ Lenovo card? It feels pretty likely. It certainly wasn’t a high-quality card struggling with 10MB/s and failing on the first day of use! I sent the three cards I bought back for a refund which the seller duly processed and decided to purchase some from a known good source. Taking no chances second time around, I bought cards direct from SanDisk.
The initial packaging is much more convincing:
Ordered from the official site, the packaging is closer to what I originally expected...
What about f3write? The speeds are much better, averaging 74 MB/s
on a quick initial test.
➜ /opt/homebrew/Cellar/f3/8.0/bin/f3write /Volumes/Untitled F3 write 8.0 Copyright (C) 2010 Digirati Internet LTDA. This is free software; see the source for copying conditions. Free space: 238.21 GB Creating file 1.h2w ... OK! Creating file 2.h2w ... 0.75% -- 74.50 MB/s -- 54:47
And if we just try our small sample, the read speed of ~90 MB/s is plenty good enough for our Pi project.
/opt/homebrew/Cellar/f3/8.0/bin/f3read /Volumes/Untitled
F3 read 8.0
Copyright (C) 2010 Digirati Internet LTDA.
This is free software; see the source for copying conditions.
SECTORS ok/corrupted/changed/overwritten
Validating file 1.h2w ... 2097152/ 0/ 0/ 0
Validating file 2.h2w ... 904385/ 0/ 0/ 0
Data OK: 1.43 GB (3001537 sectors)
Data LOST: 0.00 Byte (0 sectors)
Corrupted: 0.00 Byte (0 sectors)
Slightly changed: 0.00 Byte (0 sectors)
Overwritten: 0.00 Byte (0 sectors)
Average reading speed: 91.35 MB/s