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Another mechanism that ECS uses to ensure data integrity is to store the checksum for data written. Checksums are done per write-unit, up to 2 MB. So, checksums can occur for one object fragment for large object writes or on a per-object basis for small object writes of less than 2 MB. During write operations, the checksum is calculated in memory and then written to disk. On reads, data is read along with the checksum. The checksum is then calculated in memory from the data read and compared with the checksum stored in disk to determine data integrity. Also, the storage engine runs a consistency checker periodically in the background and does checksum verification over the entire dataset.