Data Domain: PCR post-comp for a MTree is larger than DD file system active tier size

Summary: This KB describe a symptom that DD PCR reports post-comp for a MTree that is larger than DD file system active tier size.

This article applies to This article does not apply to This article is not tied to any specific product. Not all product versions are identified in this article.
Check out other resources

Symptoms

DD Physical capacity measurement/reporting (PCM/PCR) for a MTree report post-comp size is larger than the DD file system active tier total used size.

The latest PCR report shows that the MTree located at /data/col1/avamar-123456789 has a post-comp size of 253112.8 GiB. However, the total post-comp size used by the DDFS /data partition (active tier) is only 241913.2 GiB.

sysadmin@dd123# compression physical-capacity-measurement sample show history mtrees /data/col1/avamar-123456789

MTree: /data/col1/avamar-123456789
Measurement Time      Logical Used   Physical Used   Global-Comp   Local-Comp         Total-Comp
                        (Pre-Comp)     (Post-Comp)        Factor       Factor             Factor
                             (GiB)           (GiB)                                 (Reduction %)
-------------------   ------------   -------------   -----------   ----------   ----------------
……
2021/02/27 10:00:03      62238106.        253112.8        91.31x        2.69x   245.89x (99.59%)
-------------------   ------------   -------------   -----------   ----------   ----------------

DDFS space:

sysadmin@dd123# filesys show space

GENERATED: 2021-02-27 10:45:24 PDT

Active Tier:

Resource           Size GiB      Used GiB   Avail GiB   Use%   Cleanable GiB*

----------------   --------   -----------   ---------   ----   --------------

/data: pre-comp           -   113255640.0           -      -                -

/data: post-comp   342785.4      241913.2    100872.2    71%           8030.7

/ddvar                 47.1          16.5        28.2    37%                -

/ddvar/core           984.2           0.1       934.1     0%                -

----------------   --------   -----------   ---------   ----   --------------

* Estimated based on last cleaning of 2021/02/25 09:47:35.

 

Cause

The "Physical Used (Post-Comp)" for the given MTree measured by PCR is Metadata + Physical L0 bytes. For the Metadata part, PCR reports logical LP segment size. In some workloads, such as virtual sythetic (VS) workload, LP sharing exists. As a result, the logical LP segment size can be larger than the DDFS /data partition physical size. This issue can be seen when the MTree data has a high deduplication ratio as it has high LP metadata.

From ddfs.inf0 logs, PCR job statistics

 ddfs.inf0:02/16 18:21:56.176 (tid 0x7f9928c04c20): pcr_run_job: Job (1,6) has results: logical 66827658273324768, compression 2.693984, metadata 218970311166156, num lps 16042377403, num l0s 7793825601792, l0 sum 66827658273324768, bits set 15696840, num sampled 7577743715, estimated unique num l0s with sampling 16109240, estimated unique num l0s 16495861760, bf size 38654704, files seen 38738195, paths not found 0, average l0 size 8624.134370, sampled pre lc sum 138928250366, sample post lc sum 51569813096, sampled uniq l0 count 8389415,

Physical L0 bytes = (estimated unique num l0s * average l0 size ) / compression = 16495861760 * 8624.134370 / 2.693984 = 52,806,665,450,960.36 byte
LP metadata = 218,970,311,166,156 byte
PCR “Physical Used (Post-Comp)” = 52,806,665,450,960.36 + 218,970,311,166,156 = ~253.1 TB.

 

Resolution

There is no resolution or fix for this symptom. This is how the PCR was designed and works as designed.

 

Affected Products

Data Domain

Products

Data Domain, DD OS 6.2, DD OS, DD OS 6.1, DD OS 7.0, DD OS 7.1, DD OS 7.2, DD OS 7.3, DD OS 7.4, DD OS 7.5
Article Properties
Article Number: 000184589
Article Type: Solution
Last Modified: 05 Nov 2025
Version:  4
Find answers to your questions from other Dell users
Support Services
Check if your device is covered by Support Services.