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Block Erase
In brief
Block Erase is an erasure method for flash memory such as SSDs, in which the drive’s firmware electrically resets entire memory blocks to the erased state. It is triggered by a special command and also covers areas that cannot be reached with normal write commands, such as spare blocks. The US guideline NIST SP 800-88 classifies Block Erase as a purge method.
How Block Erase works
In NAND flash memory data cannot simply be overwritten. Cells can only be written page by page but erased only block by block. With Block Erase, the controller resets all blocks of the drive, including those that are not currently in use or serve as a reserve.
This is triggered through commands of the interface:
| Interface | Command |
|---|---|
| SATA (ATA) | SANITIZE with the function BLOCK ERASE |
| SAS (SCSI) | SANITIZE with the function BLOCK ERASE |
| NVMe | Sanitize with the action Block Erase |
More on the commands in the entry Sanitize command.
Strengths and limits
On SSDs, Block Erase is more thorough than overwriting, because wear leveling and over-provisioning mean that software cannot reach all cells from the outside. The catch: whether the command is fully carried out depends on the manufacturer’s firmware and can only be verified to a limited extent from the outside. A reliable erasure therefore includes verification and a report for each drive. Which method suits which case is explained in our guide Securely erasing hard drives and SSDs.
Second IT erases SSDs using Blancco software and issues a digitally signed erasure certificate for each drive.
Frequently asked questions about Block Erase
Is Block Erase the same as Secure Erase?
Not quite. Secure Erase is an older ATA command whose implementation is determined by the manufacturer. Block Erase is a clearly defined function of the newer Sanitize command for flash memory.
Does Block Erase work on hard drives with magnetic platters?
No. Block Erase is intended for flash memory. Hard drives are overwritten, erased with an overwrite function of the Sanitize command, or physically destroyed.
How long does Block Erase take?
Usually considerably shorter than a full overwrite, often a few seconds to minutes. The exact duration depends on the drive.
Does Block Erase count as purge according to NIST?
Yes. The US guideline NIST SP 800-88 classifies Block Erase as a purge method. However, the actual effect depends on the manufacturer’s firmware. That is why verification and a report for each drive are part of it.
How is Block Erase triggered on an SSD?
Through commands of the interface. For SATA and SAS it is the Sanitize command with the Block Erase function, for NVMe the Sanitize command with the Block Erase action. The controller then resets all flash blocks of the drive.
Erase SSDs verifiably, with a certificate for each drive.
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