Assuming that shredding is performed on a single parity group, the standard shredding time for NVMe SSDs, encrypted or unencrypted, is 5 minutes per TB in the parity group. The standard shredding time for 60-TB NVMe SSDs is 1 minute per TB in the parity group. The standard shredding time for 30-TB NVMe SSDs (QLC) is 12.5 minutes per TB in the parity group. Because each volume is overwritten 3 times with dummy data, shredding requires 3 times the specified time.
Note the following:
- The assumed number of LDEVs is the maximum number of LDEVs that is allowed per parity group when each LDEV has 100 GB of capacity. If each LDEV does not have 100 GB of capacity, the required time might be longer.
- When host I/Os are performed, the required shredding time is at least 6 times that of when no host I/Os are performed.
- The required shredding time for NVMe SSDs might be a quarter or less than the expected time, depending on the internal state of the SSD.
- If there is heavy I/O load on a parity group (including a parity group not to be shredded), the shredding operation might fail. If a failure occurs, lessen the I/O load, and then perform the shredding operation again.