SC5020 Tier Capacity: Allocated Space, Free Pages and Unallocated Disks
This translates a historical SC5020 capacity discussion with Tier 1 SSD and Tier 3 10K drives. Its screenshots describe one array at one time. The source asks why Tier 1 is about 97% full and Tier 3 about 95% full even though some disk-folder space is unallocated.
Read the two different capacity views
The disk folder shows 113.53 TB total, 76.80 TB allocated, 8.09 TB spare and 28.64 TB unallocated. The 10K row holds that 28.64 TB unallocated amount. Read-Intensive SSD has only 1.06 GB unallocated. Its 99.99% used figure belongs to this disk-folder view and differs from the RAID-tier fullness figures below.
Tier and RAID figures in the source
| Tier / RAID | Total | Used | Free | Full |
|---|---|---|---|---|
| Tier 1 RAID 10 / SSD | 6.99 TB | 6.84 TB | 145.09 GB | 97.97% |
| Tier 3 RAID 10-DM / 10K | 1.48 TB | 137.50 MB | 1.48 TB | 0.01% |
| Tier 3 RAID 6-10 / 10K | 46.71 TB | 44.76 TB | 1.95 TB | 95.83% |
Tier 3’s two shown RAID allocations total 48.19 TB, but that is not the same measure as its disk-folder raw capacity or unallocated capacity. RAID protection and spare space affect the conversion between raw and usable space. The pool overview separately shows 55.18 TB total, 51.61 TB used and 3.57 TB available, with RAID overhead 1.39.
What the original answer means
The source answer says Storage Center allocates eligible backing space automatically as writes require it; a 95% full RAID allocation is not, by itself, a command to manually extend an individual RAID set. The shown Tier 3 RAID 6-10 still has 1.95 TB free, with additional 10K capacity visible at the folder level.
The source says there is effectively no SSD backing space left to allocate because only 1.06 GB remains unallocated. Automatic allocation cannot manufacture additional physical SSD capacity. If workload/service requirements need more flash capacity or performance, plan a supported SSD expansion with the exact model, software, enclosure, drive and storage-profile constraints.
Dell’s SC Series RAID explanation confirms that writes can use eligible space at other tiers/RAID levels when the preferred Tier 1 RAID 10 is full. Data Progression later moves pages according to configuration and schedules. This does not guarantee that every hot page reaches Tier 1, that free space is unlimited, or that a near-full array needs no capacity planning. Check current alerts, storage profiles, Data Progression and actual headroom.
The open Edit Disk Folder dialog shows an alert threshold of 10%, while the donut marks a 90% threshold level. These are the source’s different presentations and both are retained. Changing an alert threshold does not add storage; this article does not direct saving that dialog or perform an expansion.