Data Domain: 8 TB Disk Packs and Over Provisioning

OP is only supported on DD9400 and DD9900 starting with DDOS 7.4.

When Data Domain started offering 8 TB drive packs for external enclosures, there had to be a consideration for the performance. For example, it takes 30 four TB drives to get the same storage capacity as 15 eight TB drives. This comes with the cost of having half as many drives to spread the I/O over. The 15 eight TB drives cannot achieve the same read and write performance of the 30 four TB drives.

Over provisioning was implemented to resolve this performance shortcoming. Instead of using the full capacity of the 8 TB drives, we start by using only half of the capacity. That way we can achieve the same I/O performance of 4 TB drives. A function of how this works is that as you add more 8 TB drive packs to the system, it can use more of the overall capacity while still maintaining the performance required. Without OP enabled, the full 8 TB of storage is used at the cost of performance.

Over Provisioning uses two extra disk packs of 8 TB drives and then distributes the licensed capacity for N packs over N+2 packs. For example, a DD9400 with four packs of 8 TB drives has a licensed capacity of 240 TB (raw) (two packs of 8 TB drives). It is spread out over the four packs evenly. Each pack uses of 50% of the physical capacity.

If the user decided to add another two packs (license increases to 480 TB (raw)), then the resulting configuration uses 4/6 (67%) of each pack's physical capacity. This is done by growing the existing four packs from 50% to 67% and adding the new packs in at 67%.

You can see the following table for the DD9400 and DD9900 showing the licensed capacities, and the number of physical packs needed (including the two Over Provisioning packs):

Platform	Max Size	Drive Size (TB)		1	2	3	4	5	6	7	8	9	10
DD9400	768	8	Usable	48	96	144	192	288	384	480	576	672	768
			Raw	60	120	180	240	360	480	600	720	840	960
				50%	50%	50%	50%	60%	67%	72%	75%	78%	80%
Platform	Max Size	Drive Size (TB)		1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18
DD9900	1536	8	Usable	48	96	144	192	288	384	480	576	672	768	864	960	1056	1152	1248	1344	1440	1536
			Raw	60	120	180	240	360	480	600	720	840	960	1080	1200	1320	1440	1560	1680	1800	1920
				50%	50%	50%	50%	60%	67%	72%	75%	78%	80%	82%	84%	85%	86%	87%	88%	89%	89%

The high-density capacity license required for this to work matches the Raw value in that chart. If you have six disk packs of 8 TB, the Raw capacity is 480 TB with OP.

Some considerations when users are buying 8 TB shelves. There have been many cases where:

• User did controller upgrade pre-7.4 and OP is disabled, but the order included the two OP packs which cannot be added.
• User did controller upgrade post 7.4 and OP is enabled, but they could order 8TB packs without the two OP packs, and now they cannot use the amount they licensed.

Generally, if the 8 TB storage has not been put in-use, we prefer that OP be enabled, and if the order did not include the OP packs, that order should be returned and the correct order placed. If the storage has been put in-use, then options become more limited. Especially if OP was disabled. In that case, the only way to retain data and get to an OP enabled configuration is to replicate to new shelves with the OP configuration. This requires Dell Engineering sign-off.

To see if OP is enabled, you can check an autosupport and search for 0x10000101 in ASUP to find out if opt in dg0 is 0x10000101:
When OP is enabled:

DG:dg0 UUID:0x9ef8bbf6cf13659d MajorNr:61 MajorNrEx:62 GrpNr:0 State:Complete Status:Reassembled Index:0
    Total Disks:3 Working Disks:3 Max Disk Failures:2 Sectors:0 Options:0x10000101 Type:HeadUnit
    Pool UUID:0x0:0 Tier Type:0x1 Host SN:CNIVC0035T0591 MG UUID:0x0

When OP is disabled:

DG:dg0 UUID:0x9ef8bbf6cf13659d MajorNr:61 MajorNrEx:62 GrpNr:0 State:Complete Status:Reassembled Index:0
    Total Disks:3 Working Disks:3 Max Disk Failures:2 Sectors:0 Options:0x10000001 Type:HeadUnit
    Pool UUID:0x0:0 Tier Type:0x1 Host SN:CNIVC0035T0591 MG UUID:0x0