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July 2nd, 2025 08:05
Why is the available space of the volume displayed in the scv3020 inconsistent with that viewed in the server?
Why is the available space of the volume displayed in the scv3020 inconsistent with that viewed in the server?
The following shows that the available space in the storage is 0
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DELL-Charles R
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July 3rd, 2025 17:25
Hello,
The difference between server-reported space and storage-reported space in a Dell SCv3020 environment and which is more Accurate:
For the server’s own usage: The server view is accurate — it shows how much space the OS thinks it can use.
For actual storage availability and risk of failure: The storage GUI (DSM/Unisphere) is more accurate and authoritative.
Dell Best Practice: Always monitor storage pool usage and Replay space in DSM to avoid unexpected write failures, especially in thin-provisioned environments.
Why the Storage Shows 0 GB Free While the Server Shows Free Space
SCv3020 volumes are typically thin provisioned, meaning the storage system allocates physical space only as data is written. The server sees the full logical volume size (e.g., 2 TB), but the storage system only tracks actual usage.
Dell SC Series uses Replays (snapshots) that consume space in the background. These are not visible to the server but can significantly reduce available space on the storage system
The SCv3020 uses dynamic RAID levels (e.g., RAID 10 for active data, RAID 5/6 for cold data). This means storing 1 TB of data might require 2–3 TB of physical space depending on the profile .
If any single volume reaches 100% of its allocated space, the SC system may enter emergency mode, even if other volumes or the pool have space
Recommended Actions
Unfortunately this isn't something you can do by yourself. You might need the help of the support as they need to remote in to check on the storage and probably delete the snapshot storage. It is not advisable to delete the snapshots by your own as this will corrupt the whole storage data.
DELL-Chris H
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July 2nd, 2025 12:13
Stevencao,
When the available space of a volume on a Dell SCv3020 storage array appears inconsistent between the storage system and the connected server, it typically results from differences in how space is reported, allocated, or reserved at different layers of the storage stack.
Some things you may want to look into would be
1. Thin Provisioning
The SCv3020 supports thin provisioning, which allows volumes to appear larger to the host than the physical space actually allocated.
The storage system may show 0 GB free if the physical pool is exhausted, even though the server still sees available space in the volume.
2. Snapshot and Replay Reservations
SC Series arrays reserve space for snapshots (replays) and data protection policies.
This reserved space reduces the usable capacity at the storage level but is invisible to the host.
3. Volume Mapping and Host OS Caching
The host OS may cache volume metadata or not immediately reflect changes in available space.
Filesystem-level space (e.g., NTFS, ext4) may differ from block-level space reported by the SAN.
4. Unmapped or Orphaned Blocks
If the host deletes data but does not issue SCSI UNMAP/TRIM commands, the storage array may still consider the space as used.
This is common in older OS versions or when UNMAP is disabled.
5. Volume Quotas or Limits
The SCv3020 may enforce volume-level quotas that cap usage regardless of the pool’s total capacity.
Let me know if this helps.
Origin3k
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July 2nd, 2025 14:00
Because a Volume from Compellent, its by design, is always overprovisioned. All kind of data protection (Raid Levels, Snapshots,....) and overhead comes on top and on the fly when the server starts writing data.
Regards,
Joerg
Stevencao
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July 3rd, 2025 15:26
@DELL-Chris H
In this case, how can I check how much free space is actually available? Is it more accurate to display it on the server or in the storage GUI?