Low write speed on Ultra 512Gb micro SD

Memory Cards SD | microSD | CFast | CFexpress | CompactFlash
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I bought a used SanDisk Ultra 512Gb micro SD on eBay. It writes at 7-8 Mb/s which I think is absolute rubbish. It reads at about 60 Mb/s.

I have other makes of card which give me write speeds of around 40-50 Mb/s. None are top of the range Extreme or Pro type cards.

Is my Ultra writing normally or is it a dud card?

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Hi @Alpaca

Have you checked our knowledge base articles?
(Get Support for Your SSDs and Flash Products | SanDisk)

Try this one.

Have you opened a Support Case?
If not, contact SanDisk Technical Support for assistance.
(Contact Support | SanDisk)

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Thank you. I bought it “Used” on eBay, so can I claim against SanDisk?

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"Hi @Alpaca ,

Since the card was bought used on eBay, it’s likely not covered by SanDisk’s warranty. The slow write speed might mean the card is damaged or fake. You can check if it’s real using SanDisk’s Memory Zone app or similar tools. If it’s fake or faulty, try contacting the eBay seller or opening a dispute. Let me know if you need help!"

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Hi Helly. Thank you for your reply.

The app SD Insight says it’s a SanDisk made in July 2024.

Alan’s True SD Capacity/Speed shows a write speed around 7Mb/s. During the write test the speed fluctuates constantly, quite unlike my known good cards of other makes. Real life file transfer shows a write speed starting just in double figures but slowing to about 7Mb/s. This is rubbish.

Read speed is around 60Mb/s with zero errors. Capacity is over 300Gb and counting so not a smaller card.

So I think it’s a genuine SanDisk. I have told the eBay seller and he says the Ultra is nowhere near as fast as some other makes, and this is normal.

Of the 512Gb micro SD cards in the lower price range, i.e. not the top priced heavy duty “Pro” type cards, the SanDisk Ultra is the dearest. Cheaper cards write at 40-60 Mb/s when I use them. I cannot believe that the more expensive SanDisk Ultra is made to run at only 15% of its competitors’ speed.

Is this performance normal for a 2024 Ultra, or have I got a dud? Comments on earlier threads refer to much older cards.

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Thank you. I bought it used on eBay. I use it in my Android tablet for which it is correctly formatted to exFAT.

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The card you are describing has 10-20 MBps for larger capacities like 512GB and a read speed of up to 100 MBps. But a write speed of 7-8 Mbps for a 512GB card is unusually slow, even for this model.
Since you bought it used on eBay, it’s worth verifying the card isn’t false. False cards often have incorrect capacities and have abnormally low write speeds. You can use tools like H2testw (Windows) or F3 (Mac/Linux) to test the card’s actual capacity and performance. Try to format it and see if you can regain the full capacity of the card.