Data Domain: DD6300 5-Disk Upgrade Shows Incorrect Expandable Capacity (2.18 TiB)

Summary: When expanding a DD6300 system from 7 to 12 disks, the filesys expand command incorrectly reports only 2.18 TiB of additional capacity. This is a false reading caused by a miscalculation in DDOS. The issue affects all DDOS versions and does not impact usable capacity. ...

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Symptoms

  • DD6300 upgraded from 7 to 12 disks.
  • Additional five disks added to the Active Tier using #storage add.
  • #filesys expand reports only 2.18 TiB available for expansion.
  • The expected capacity increase is approximately 11 TiB (from ~14.5 TiB to ~24 TiB).
  • No DDOS patch available; issue confirmed and workaround provided.
  • Affected systems: DD6300 (all DDOS versions).
  • Other All-in-One systems may encounter similar behavior if cache tier disks are present in the head/controller unit.

Cause

DDOS incorrectly calculates expandable capacity by scanning for the smallest partition (ppart) across all disks in the head unit. In DD6300 systems, this is often the SSD used for the cache tier, with a ppart size of 745.22 GiB.

The system then calculates usable capacity based on this smallest partition:

  • Three data disks (5 minus 2 parity) × 745.22 GiB = 2235.66 GiB
  • 2235.66 GiB ÷ 1024 = 2.18 TiB

This value is incorrectly presented as the maximum expandable capacity.

Resolution

This is a false capacity report. The system expands correctly despite the misleading message.

Workaround:

  1. Confirm that the five new disks are added to the Active Tier and show as SPARE in #disk show state.
  2. Proceed with #filesys expand and accept the prompt despite the 2.18 TiB message.
  3. Filesystem is expanded to the correct total capacity (~23.87 TiB).

Example scenario and CLI Output:

1.) The extra five disks are installed and presented as 'Unknown' status, as expected, with #disk show state:

2.) Disks are successfully added to the Active Tier using #storage add disks 1.8 1.9 1.10 1.11 1.12 tier active    

The 5x new disks have a SPARE status:

sysadmin@systemname# disk show state
Enclosure   Disk                                       
             1  2  3  4  5  6  7  8  9  10 11 12 13 14 
---------   -------------------------------------------
1            .  .  .  s  .  .  .  s  s  s  s  s  .  .  
---------   -------------------------------------------
3.) The final step (#filesys expand) reports that the Filesys capacity is increased by only 2.18TiB (instead of an expected ~11TiB): 
sysadmin@systemname# filesys expand 
The filesystem will be expanded approximately by 2.18 TiB.
        Are you sure? (yes|no) [no]: yes

ok, proceeding.

########################################### [100%]
The approximate size of the filesystem is 23.87 TiB.
sysadmin@systemname#

Affected Products

Data Domain

Products

Data Domain, Data Domain Deduplication Storage Systems, DD6300 Appliance
Article Properties
Article Number: 000052485
Article Type: Solution
Last Modified: 13 Oct 2025
Version:  5
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