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Knowledge Base

FAQ-The Storage Capacity of an S5500T V2 Is Incorrect

Publication Date:  2018-10-17  |   Views:  382  |   Downloads:  0  |   Document ID:  EKB1001923990


Issue Description

In an S5500T V2 storage system, 50 x 4 TB NL-SAS disks are configured into 8D+2P RAID 6. The hot spare policy has been manually set to a low configuration. However, the actual available capacity is only 131 TB, with a loss of nearly 50 TB available capacity.


1. Adjust the hot backup policy. You can only run the change disk_domain general disk_domain_id=? { name=? |tier0_hotspare_strategy=? |tier1_hotspare_strategy=? | tier2_hotspare_strategy=? } command on the CLI. You are not allowed to adjust the hot backup policy using DeviceManager.

2. Capacity usage details are as follows:

Each disk:
4000 GB * 1000 * 1000/1024 = 3906250 MB                                              // The vendor-claimed 4000 GB is converted into MB as follows:
3906250 MB – 256 MB = 3905994 MB                                                     // 256 MB indicates the write hole space of a disk.
3905994 MB * 93.8% = 3663822.372 MB                                             // 5.2% of space acts as the metadata space, and 1% of space is reserved to improve system performance and disk balancing.
3663822.372 MB * 48 (two hot spare disks are subtracted)/1024/1024 = 167.72 TB               // The hot spare policy is low. Therefore, two spare disks are used.
167.72 TB * 80% = 134.2 TB                                                                     // The actual available capacity of RAID 6-10 is 80%.

The calculation result is close to the value obtained from the tool. The actual capacity displayed in the ISM running on the SVP is similar.