WAFL NetApp

What is WAFL?

WAFL, or Write Anywhere File Layout, is a proprietary file system developed by NetApp for its storage appliances. It is designed to support large, high-performance RAID arrays, enable quick restarts without lengthy consistency checks after a crash or power failure, and allow rapid filesystem growth.

Why WAFL is 4KB in Size?

In NetApp, FC and SAS drives uses 520-byte sectors and each 4KB block is made up of eight sectors. The last 8 byte is reserved for the BCS.

Note: Here BCS means, Block Checksum that is used to ensure data integrity by detecting corruption in stored data blocks. When data is written to a disk, a checksum is generated and stored alongside the data. Upon retrieval, the system recalculates the checksum and compares it to the stored value—if they match, the data is intact; if not, corruption is detected.

Therefore, 520-bytes now becomes 512-bytes that when multiplied by the 8 becomes 4096-bytes that is the size of NetApp's WAFL Block.

In SATA drives, NetApp uses BCS 8/9 checksum methods to basically format the disk. This means that each 4KB block is made up of 9 sectors out of which only 8 sectors are used to store the user's data. This same is used in the case of the SSD which again uses the 512-bytes sectors to store the data.

Additionally, there are some factors or reservations in NetApp:

1. 10% WAFL system reserve.

2. 5% aggregate snapshot reserve.

3. 20% default volume snapshot reserve.

This is how WAFL block in NetApp is calculated. For more information or deep dive in this topic do comment. I will go deeper dive in this topic.

Thanks!!