Reduced capacity on Sandisk MicroSD cards

[Delta]

I've been using 32GB Sandisk cards (Sandisk Ultra microSDHC UHS-I, class 10, to be precise) for my Raspberry Pi projects, and once I had everything set up nicely I took a backup image of the SD card and use that same image for each new project.
I had been buying the cards as and when needed off-the-shelf in my local Tesco (large supermarket chain) for £14 a pop, and hadn't had any problems.

Then I bought one from eBay (just under a tenner) from an "Official Sandisk eBay partner" in the UK.  I noticed the packaging was slightly different, which raised suspicions, and then when I tried to write the image to the card I found its capacity was 810MB less than the cards I had been using! 

I opened I request on eBay, and fired off a message to the seller explaining that this item was a fake.

Next time I was in the supermarket, I bought a "proper" card, and the packaging seemed normal (the same as previous good cards bought there), yet when I got it home - exactly the same! 810MB smaller than the old cards!

So either Sandisk themselves have reduced the capacity, or fakes have found their way into the mainstream supply lines...

(I've shrunk my image so I can use these new cards, but I'm still a bit perplexed and pissed off with the whole thing)

[kripton2035]

IMHO your supermarket also bought fakes ...

[hans]

https://dashcamtalk.com/forum/threads/two-32gb-sd-cards-different-capacities-after-formatting.11690/

One reason is that during a low-level format, all the sectors on the card are examined. If any are "bad", then they are marked as bad and are unusable--thus, reducing the amount of available capacity.

That could be a logical explanation. Still doesn't take away the fact that a new card should be 100% rated capacity and not have bad sectors affect the capacity in orders of magnitude like this.

[rstofer]

Have you checked for a hidden partition?  Maybe try fdisk?

[Delta]

Have you checked for a hidden partition?  Maybe try fdisk?

I thought then when you wrote an image to a card, you are working at a level lower than the partition table, so this couldn't be an issue?  (For example, my image contains two separate partitions, so the image must incorporate the partition table)

[nfmax]

In my experience the exact capacity of flash thumb drives and SD cards is variable, even from new. The flash devices used aren't perfect and they expect a few bad blocks, which are mapped out by the device firmware. The stated capacity is the maximum value. On the other hand SSD drives seem to state the minimum capacity, keeping their spare blocks in reserve. As they are higher performance devices, they tend to have extra blocks dedicated to buffereing and caching anyway.

Of course there are fakes, which may have sizes bearing no relation at all to the stated capacity

[rstofer]

I've been using 32GB Sandisk cards (Sandisk Ultra microSDHC UHS-I, class 10, to be precise) for my Raspberry Pi projects, and once I had everything set up nicely I took a backup image of the SD card and use that same image for each new project.
I had been buying the cards as and when needed off-the-shelf in my local Tesco (large supermarket chain) for £14 a pop, and hadn't had any problems.

Then I bought one from eBay (just under a tenner) from an "Official Sandisk eBay partner" in the UK.  I noticed the packaging was slightly different, which raised suspicions, and then when I tried to write the image to the card I found its capacity was 810MB less than the cards I had been using! 

I opened I request on eBay, and fired off a message to the seller explaining that this item was a fake.

Next time I was in the supermarket, I bought a "proper" card, and the packaging seemed normal (the same as previous good cards bought there), yet when I got it home - exactly the same! 810MB smaller than the old cards!

So either Sandisk themselves have reduced the capacity, or fakes have found their way into the mainstream supply lines...

(I've shrunk my image so I can use these new cards, but I'm still a bit perplexed and pissed off with the whole thing)

That's true when using 'dd' but I'm not familiar with the program you seem to be using.

I just looked at an fdsik of an SD card and when I use 'p' to print the partition table, I get a LOT of information on the physical disk size.  It might be fun to compare two 'identical' SD cards and see what shows up.

My 8GB card shows 7,948,206,080 bytes or 15,523,840 sectors of 512 bytes.  fdisk shows this as 7.4 GiB which is short of even the disk industry's opinion on the size of a gigabyte.

You are right about /dev/sdc being the entire SD card.   My only experience with writing images to drives is via 'dd'.  I do a lot of that kind of thing when I make CF images of IBM1130 drives, a completely unintelligible file system as far as a PC is concerned.  But as long as I have the image in a file, 'dd' will write it.

[Delta]

I'm using "Disks", the Gnome disk utility.  I'd hazard a guess that it probably uses

Code: [Select]

dd to do its stuff.

As I've now had two cards that were both 810MB too small, I think it's too much of a coincidence to be caused by random bad blocks / flash cells...

I might contact Sandisk to see what they say...

[Ampera]

I've been using 32GB Sandisk cards (Sandisk Ultra microSDHC UHS-I, class 10, to be precise) for my Raspberry Pi projects, and once I had everything set up nicely I took a backup image of the SD card and use that same image for each new project.
I had been buying the cards as and when needed off-the-shelf in my local Tesco (large supermarket chain) for £14 a pop, and hadn't had any problems.

Then I bought one from eBay (just under a tenner) from an "Official Sandisk eBay partner" in the UK.  I noticed the packaging was slightly different, which raised suspicions, and then when I tried to write the image to the card I found its capacity was 810MB less than the cards I had been using! 

I opened I request on eBay, and fired off a message to the seller explaining that this item was a fake.

Next time I was in the supermarket, I bought a "proper" card, and the packaging seemed normal (the same as previous good cards bought there), yet when I got it home - exactly the same! 810MB smaller than the old cards!

So either Sandisk themselves have reduced the capacity, or fakes have found their way into the mainstream supply lines...

(I've shrunk my image so I can use these new cards, but I'm still a bit perplexed and pissed off with the whole thing)

That's true when using 'dd' but I'm not familiar with the program you seem to be using.

I just looked at an fdsik of an SD card and when I use 'p' to print the partition table, I get a LOT of information on the physical disk size.  It might be fun to compare two 'identical' SD cards and see what shows up.

My 8GB card shows 7,948,206,080 bytes or 15,523,840 sectors of 512 bytes.  fdisk shows this as 7.4 GiB which is short of even the disk industry's opinion on the size of a gigabyte.

You are right about /dev/sdc being the entire SD card.   My only experience with writing images to drives is via 'dd'.  I do a lot of that kind of thing when I make CF images of IBM1130 drives, a completely unintelligible file system as far as a PC is concerned.  But as long as I have the image in a file, 'dd' will write it.

I rarely use FDisk unless I am working with MS-DOS on an 80486. GParted is honestly the only functioning partition manager. I don't think there is a partition it CAN'T manage (Except Windows Dynamic Volumes, the bane of my bloody existence).

I've often seen stuff like this where I can have a 1TB drive, and get 9XX of storage on it, it's confusing but it has to do with drive formats and allocation and whatever it is.

[Delta]

Here's a brand new card straight out the packet from eBay.  It is 810MB too small to take the original image,

Code: [Select]

:~$ sudo fdisk -l /dev/sdc
Disk /dev/sdc: 29 GiB, 31104958464 bytes, 60751872 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x00000000

Device     Boot Start      End  Sectors Size Id Type
/dev/sdc1        8192 60751871 60743680  29G  c W95 FAT32 (LBA)
Unfortunately I don't have any of the original "good" cards lying around.  I'll see if can mount the image and get any info from that...

[Delta]

Here is the original image, mounted as a device...

Code: [Select]

Disk /dev/loop0: 29.7 GiB, 31914983424 bytes, 62333952 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x5d98613b

Device       Boot  Start      End  Sectors  Size Id Type
/dev/loop0p1 *      8192   124927   116736   57M  e W95 FAT16 (LBA)
/dev/loop0p2      124928 62332927 62208000 29.7G 83 Linux


[mtdoc]

An excellent tool for checking the integrity/authenticity of SD cards (or thumb drives) is H2testw

[RGB255_0_0]

I have a 32GB Sandisk uSD from about 4 years ago and it's 31,914,983,424.

Perhaps Sandisk have shaved off a few costs. Or there's a trojan in their supply line

[suicidaleggroll]

I have a 32 GB Sandisk Ultra uSD from a few years ago, it's 31,914,983,424 as well.

[Delta]

An excellent tool for checking the integrity/authenticity of SD cards (or thumb drives) is H2testw

I've just ran the Linux version of that utility, and the reported capacity is genuine.  That's something at least...

Code: [Select]

  Data OK: 28.96 GB (60727232 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: 31.40 MB/s

I'm still intrigued as to the why the capacity has been reduced; and whether these cards are genuine or not...

If anyone buys a new Sandisk Ultra MicroSD card, please check its capacity and post here!

[SeanB]

They probably changed supplier of the raw memories or the controller, and the new supplier is giving a smaller size flash, so they have to shave off near 1G to handle the spare cells needed for wear levelling, a wear level table, and probably a small chunk of flash to store the microcontroller on the unit firmware.

[C]

DD
If you are working with sectors, what happens when you read a bad sector, go to write good data in a bad sector.
At this level, you are below the bad sector information that a file system has. If you change where data is written then you are out of sync with file system.
To clone you need a ZERO error read followed by a ZERO error write by DD.
 FDisk & GParted report the start and end blocks for a partition there is no separation of good blocks vs bad blocks. 

And at some point hidden replacement sectors will be used up.

[CJay]

I've been using 32GB Sandisk cards (Sandisk Ultra microSDHC UHS-I, class 10, to be precise) for my Raspberry Pi projects, and once I had everything set up nicely I took a backup image of the SD card and use that same image for each new project.
I had been buying the cards as and when needed off-the-shelf in my local Tesco (large supermarket chain) for £14 a pop, and hadn't had any problems.

Then I bought one from eBay (just under a tenner) from an "Official Sandisk eBay partner" in the UK.  I noticed the packaging was slightly different, which raised suspicions, and then when I tried to write the image to the card I found its capacity was 810MB less than the cards I had been using! 

I opened I request on eBay, and fired off a message to the seller explaining that this item was a fake.

Next time I was in the supermarket, I bought a "proper" card, and the packaging seemed normal (the same as previous good cards bought there), yet when I got it home - exactly the same! 810MB smaller than the old cards!

So either Sandisk themselves have reduced the capacity, or fakes have found their way into the mainstream supply lines...

(I've shrunk my image so I can use these new cards, but I'm still a bit perplexed and pissed off with the whole thing)

That's true when using 'dd' but I'm not familiar with the program you seem to be using.

I just looked at an fdsik of an SD card and when I use 'p' to print the partition table, I get a LOT of information on the physical disk size.  It might be fun to compare two 'identical' SD cards and see what shows up.

My 8GB card shows 7,948,206,080 bytes or 15,523,840 sectors of 512 bytes.  fdisk shows this as 7.4 GiB which is short of even the disk industry's opinion on the size of a gigabyte.

You are right about /dev/sdc being the entire SD card.   My only experience with writing images to drives is via 'dd'.  I do a lot of that kind of thing when I make CF images of IBM1130 drives, a completely unintelligible file system as far as a PC is concerned.  But as long as I have the image in a file, 'dd' will write it.

I rarely use FDisk unless I am working with MS-DOS on an 80486. GParted is honestly the only functioning partition manager. I don't think there is a partition it CAN'T manage (Except Windows Dynamic Volumes, the bane of my bloody existence).

I've often seen stuff like this where I can have a 1TB drive, and get 9XX of storage on it, it's confusing but it has to do with drive formats and allocation and whatever it is.

Dynamic volumes are fairly easy to deal with but there's no easy official way to do some things.

The lack of capacity on a 1TB drive is also to do with the drive manufacturers 'redefining' the GB

[Monkeh]

Drive manufacturers are using the correct units. 'everybody' (that is: Microsoft) uses the wrong units.

[CJay]

Drive manufacturers are using the correct units. 'everybody' (that is: Microsoft) uses the wrong units.

True, but the only place I've seen GiB used on a PC was on a fairly recent Linux distro, Apple and pretty much every hardware manufacturer who isn't in the storage media business use GB to mean GiB, MS are far from the only abuser.

[Kilrah]

Apple actually uses GiB, but label it as GB to avoid confusion.

Those differences also apply to hard drives, friend had 2 4TB drives of the same manufacturer but different "variant" and one had 13GB less.

[Monkeh]

Apple actually uses GiB, but label it as GB to avoid confusion.

Errr.. no, they don't.

[Kilrah]

Errr.. no, they don't.

? 

[Monkeh]

Notice how Windows says '228GB' (ignoring your locale issues), and OS X says '245.21GB'. And how the real capacity is 245,202,157,568 bytes.

Also: https://support.apple.com/en-us/HT201402

Storage device manufacturers measure capacity using the decimal system (base 10), so 1 gigabyte (GB) is calculated as exactly 1,000,000,000 bytes.

<snip>

In Mac OS X v10.6 and later, storage capacity is displayed as per product specifications using the decimal system (base 10). A 200 GB drive shows 200 GB capacity

[Kilrah]

Yeah, got GiB and GB swapped again.

Shows how stupid the whole thing is.