SD Card - Bad Block Screening - Using large SD cards in the camera

Use of larger SD cards in the MOBOTIX cameras.

These days, micro SD cards are available far beyond the terrabyte limit. These allow extended local recording in the camera itself and promote the use of the decentralised MOBOTIX idea that the camera records the data independently and autonomously and does not require an external recording server.

MOBOTIX AG has been using a pre-installed SD card or micro SD card in every camera for over 20 years. We use a sophisticated check that registers “strange” write behaviour and reports it to the user. Above a certain number of incorrect write accesses, the SD card is no longer considered reliable for a security application and a corresponding failure message is sent to the user as it is assumed that the SD card is worn out.

Consequently, the camera will stop recording to the faulty camera and the user must replace the card.

In the flash memory market in particular, production costs play a major role in pricing; with standard SD cards that are produced for the mass market, any additional costs must be minimised in order to remain attractive in terms of price. Bad block screening is very time-consuming and is usually handed over to the end customer.

Bad Block Screening

Defective areas of the SD card can be recorded in a list of bad blocks and are not used in operational use. This ensures that only “functioning” areas are addressed during write access to the card and “defective areas” are not addressed at all.
Depending on the size of the SD card, bad block screening can take several hours per SD card.

The approach of the SD card manufacturers is that the customer can perform a low level formatting of the SD card and all bad blocks are recognised and recorded (marked) in the SD card to ensure smooth operation.

In the Admin area, the camera offers Secure Formatting and Low Level Formatting, whereby each cell area of the SD card is written to and a Bad Block is processed. Compared to the Quick formatting of the camera, the SD card is “only” partitioned and not every cell area is checked/written to.
The difference between Quick and Safe (Slow) formatting depends on the SD card capacity and can be in the range of minutes for Quick format and in the range of hours/days for Safe format (1.5 T bytes is in the range of 50 hours).

Practical tip

  1. Format the SD card once with Quick Format (avoids possible boot problems in the subsequent Secure Formatting (secure deletion - slow), e.g. if a power interruption occurs during the Secure Format).
  2. Perform the Secure Formatting.

Please note: This may take several hours and the camera will not be responsive during this time.

In our SD card whitelist, we list the times for Quick and Safe Format in detail. A Samsung TLC SD card with 256 GB, for example, takes 15 hours.

  1. As soon as the slow formatting has been completed, the camera can be used for SD card recording.

Methods / tools to perform SD card bad block screening

  1. Via the camera web interface with slow formatting (“secure delete - slow”):
  1. With the MOBOTIX Management Centre MxMC (SD Card Manager – “Secure Format”). The advantage here is that SD card formatting can be initiated on several cameras at the same time!

Screenshot 2023-03-15 at 15.37.34

  1. With the PC and SD card reader and PC storage media tools that check the storage medium and recognise the bad blocks, e.g:

Praxis Tip: With fast USB 3.0 card readers, bad blocks can be recognised faster and also in parallel with several card readers.

Important: In all cases, SD card recording must then be activated in the camera.
In case 3 with the external tools a quick formatting (in the camera or using MxMC) must then be performed to create the MOBOTIX MxFFS partition on the SD card.