In this article, we estimate the performance of the storage system controllers of the new EMC VNX7600 for different workload profiles, as well as other parameters of IOPS per GHz, IOPS per GB.
All the performed calculations are based on the methodology described in the article «Methodology of IOPS Estimation».
Let’s gather all necessary information needed to a calculation.
- The frequency of processor cores – 2,2 GHz.
- The number of cores on the one controller – 8.
- The sum frequency calculation – 8 x 2,2 GHz = 17,6 GHz. At this stage we can get a rough estimation of the IOPS for one controller. To do this, it is necessary to use the relation between the number of IOPS and sum frequency of the controller. This value is specified in the methodology (10000 IOPS / GHz). Let’s multiply 17,6 GHz x 10000 IOPS / GHz, we obtain a rough estimation 176000 IOPS per controller. Thus, the performance of a pair of controllers is equal to 352000 IOPS. We can use these rough estimates for self-examination.
- We take information about recommended configurations of RAID groups in the «View on new EMC VNX2 series»:
- RAID 5 SSD are used in the configuration 4+1 or 8+1.
- RAID 5 SAS are used in the configuration 4+1 or 8+1.
- Max disk drive quantity for the VNX7600 is 1000.
Now we need to estimate the maximum number of Flash drives, which will be aligned with the performance of controllers.
In general, the basic idea is to carefully calculate the number of Flash drives that does not overload the SAS chips which are responsible for Backend, and to carefully consider the scaling of processor power.
General information about number of SAS chips and SAS ports for VNX2 controllers is given in the article «View on new EMC VNX2 series». And in the article «IOPS Estimation for EMC VNX5400», we evaluated the number of Flash drives in the configuration when the controller uses a single SAS chip with 4 ports. It’s about 50 Flash drives. In the case of VNX7600, the number of chips SAS (and SAS ports) doubles. Thus, we get a rough estimate of 100 Flash drives for VNX7600.
It is also worth to consider that SAS chips always have an additional performance reserve.
If we compare the sum frequencies of CPU cores for VNX5400 and VNX7600 controllers, we see that the sum frequency for VNX7600 is up 2,44 times greater than that of VNX5400. I.e., we see that there is a potential reserve of performance that can provide support for more quantity of Flash drives.
In order to get a more accurate estimate of the number of Flash drives, let’s consider VNX7600 system in All Flash configuration. The table is presented on EMC website with information about All Flash systems VNX-F7000 and VNX-F5000, which are based on VNX7600 and VNX5400. There it’s specified that the VNX-F7000 system can be used 135 Flash drives eMLC 1.6TB. Flash drives are used with high-density shelves (120 x 2.5″).
We know that the sum frequency for VNX7600 is up 2,44 times greater than that of VNX5400. Therefore, multiplying the estimation of Flash drives quantity for VNX5400 by this factor, we obtain another estimation of Flash drives quantity for VNX7600, i.e. 50×2,44 ~ 122 drives.
In general, we take the average of these 3 estimations, because we don’t want to strain our mind thinking about the spread of these evaluations. As a result we get (100+122+135)/3 = 119 Flash drives. Let’s round to 120. We will use this quantity in our calculations.
The use of two types of Flash drives (SLC and MLC) in VNX2 is possible, so we will make two configurations:
- SLC drives 200GB for Fast Cache (max 42) and MLC drives 800GB
- MLC drives 800GB.
The estimation for max IOPS (Cache Read Miss)
Let’s set the basic values for the estimation:
- Read operations – 99%.
- The configuration for Fast Cache (SLC) – RAID10 1+1.
- The quantity of groups – 21.
- The configuration for MLC drives – RAID5 4+1 or 8+1.
- The configuration for SAS 10K – RAID5 4+1 or 8+1.
As a result we got such a calculation without Fast Cache:
Max IOPS is 531262.
Max IOPS for one controller is 265631.
The ratio IOPS per GHz is about 15093.
The ratio IOPS per GB is 1,23.
Real Flash storage capacity is about 67 TB.
Real SAS 10K storage capacity is about 355 TB.
Let’s compare this result with a rough estimation, which we did in the beginning of this article. Then we got 176000 IOPS for one controller. The difference with the new result is 89631 IOPS. This is about 50% of the rough estimation. This suggests that the ratio of IOPS per GHz for the system is higher than the ratio – 10000 IOPS per GHz, which we used in the calculation.
The estimation with Fast Cache:
Max IOPS is 534088.
Max IOPS for one controller is 267044.
The ratio IOPS per GHz is about 15526.
The ratio IOPS per GB is 1,298.
Real FastCache capacity is 3752 GB
Real Flash storage capacity is about 43 TB.
Real SAS 10K storage capacity is about 355 TB.
The IOPS estimation for DB like workload (Cache Read Miss)
Initial parameters are the same, but the percentage of read operations is different. Typical ratio between read and write operations is equal to 70/30 for databases (OLTP workload).
Max IOPS (DB like) is 288000.
Max IOPS for one controller (DB like) is 144000.
The ratio IOPS per GHz is about 8372.
The ratio IOPS per GB is 0,667.
An estimation with Fast Cache:
Max IOPS (DB like) is 323709.
Max IOPS for one controller (DB like) is about 161865.
The ratio IOPS per GHz is about 9411.
The ratio IOPS per GB is 0,787.