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OceanStor 5600 V3 storage pool capacity issue

Publication Date:  2016-09-29 Views:  113 Downloads:  0
Issue Description

Storage Model:OceanStor 5600 V3

Version:V300R001C10

Issue Description:

The customer addednew 10 * 6TB Disks. But can ONLY create a storage pool of from ( 20 TB to 26
TB
). The client is expecting to get approximately 50 TB usable.


Alarm Information
None
Handling Process



First:

The disk capacity defined by disk manufacturers is different from that calculated by operating systems. As a result, the nominal capacity of a hard disk is different from that displayed in the operating system.


Disk capacity defined by disk manufacturers: 1TB=1000GB, 1 GB = 1,000 MB, 1 MB = 1,000 KB, 1 KB =1,000 bytes.

 Disk capacity calculated by operating systems: 1TB=1024GB,1 GB = 1,024 MB, 1 MB = 1,024 KB, 1 KB = 1,024 bytes.

So the  actual available capacity is calculated as follow:    6TB x(1000/1024)×(1000/1024)×(1000/1024)×(1000/1024)≈5.457TB

Second:

Capacity reserved by the system. 

  Metadata : 5.2% of each disk's capacity. 

  Capacity reserved for improving system performance and disk load balance:  1% of each disk's capacity.

Capacity used by write hole: 256 MB of each disk's capacity.

Capacity used by system information: 577 MB of each disk's capacity.

The capacity used by write hole and system information is only 833MB,it is very small compare with 6TB,we can ignore it when calculate the total size.

So the disk size after reserving some capacity by the system is calculated as follow:
5.457TBx(1-5.2%)x(1-1%)=5.122TB

Third:

Integrated capacity

During disk formatting, the default sector size is 520 bytes, 8 bytes of which are
used for storing parity data. The integrated capacity usage is 98.46% (512/520).

So the disk size after integrated capacity is 5.122TBx512/520=5.043TB

The customer add 10 6TB NL_SAS disk, the storage system will take 1 disk size as hot spare space, so the total size available is 5.043TBx9=45.387TB.


If you want to create Raid6(4D+ 2P): The disk utilization is about 66.67%,so the total available capacity should be 45.387TBx66.67%=30.27TB.

But as per customer feedback, the available capacity is only 20.029TB.



This is another issue:

In Huawei storage system, we don’t suggest put different size disks in the same disk domain, and there is a limitation:

If we add different size disks in the same disk domain ,each size disk quantity must be at least 11 disks, otherwise the system will recognize each disk by the smaller size.

In our case, we can find 10 6TB NL_SAS disks had been added in the disk domain.


And already the disk domain had 4TB NL_SAS disks.



So the system will recognize these 10 disks as 4TB,not 6TB,finally the total available capacity is only 20.029TB.









Root Cause


1:The disk capacity defined by disk manufacturers is different from that calculated by operating systems.

2:Storage system will reserve some capacity.

3:When adding different size disks in the same disk domain ,each size disk quantity must be at least 11 disks, otherwise the system will recognize each disk by the smaller size.

Solution

explain to customer why the available storage pool size is only 20TB.

Add one more 6TB NL_SAS disk into the disk domain.

Suggestions
None.

END