Two methods and examples for connecting to the IBM ds4800 storage expansion Cabinet

I. Two Methods for connecting to the IBM ds4800 storage expansion Cabinet

The IBM ds4800 storage can be used to add expansion cabinets. When the expansion cabinet is added, a new drive loop pairs is added, which is called horizontal scaling ). conversely, when an expansion cabinet is added to an existing drive loop, we call it vertical scaling ).

When performing horizontal expansion, try to distribute the expansion Cabinet to all drive loops as much as possible, so that the expansion Cabinet maintains a balance in the number of drive loops. in addition, try to keep the Luns distribution Horizontal, which can match the distribution of the expansion cabinet.

Vertical Scaling may be unbalanced. For example, if you only use two loops (like ds4500) and add eight exp710s to each loop, you will not be able to achieve optimal configuration through scaling. You can also use the vertical distribution of Luns in combination with the exp710 extension. The two extension modes have the following advantages:

1. Advantages of horizontal scaling

· Maximum availability-deploy Luns evenly across four drive loops as much as possible, instead of two loops.
· Maximum bandwidth-fully distributed Luns (Luns uses hdds that exist on four drive loops ), therefore, the maximum bandwidth of up to 3,200 MB/sec is used (the maximum bandwidth of each drive loop is 800 mb/sec ).

2. Advantages of Vertical Scaling

· Dedicated bandwidth-place all Luns on a drive loop to ensure they have a maximum bandwidth of 800 mb/sec. if you distribute a lun across all drive loops, The Lun must compete for bandwidth with other Luns. this may cause performance degradation. However, this may change depending on your environment and workload.

· Optimized use of A 2/4 Gbit/s hybrid environment-the ds4800 can support 2 Gbit/s or 4 Gbit/s bandwidth for different drive loops. this will allow you to use the latest 4 Gbps technology, but you can also upgrade to the customer's existing 2 Gbps environment. in this case, it is best to place the Luns of your cross-expansion cabinet at the same rate. Therefore, in a mixed environment with 2 and 4 Gbps, horizontal scaling is not a recommended practice.

The bandwidth of each drive loop pair (per loop pair) of 800 mb/sec refers to the maximum bandwidth in a completely 4 Gbps environment, which means you must use 4 Gbps hdds, 4 Gbps exp units, and 4 Gbps SFPS. If you do not use a completely 4 Gbps component, the bandwidth of ds4800 will only work in the rate mode of the lowest rate component of all components. Because ds4800 only supports 2 Gbps and 4 Gbps connections, and does not support 1 Gbps connections, the working rate of hybrid components is 2 Gbps. In a drive loop pair, it is best to use only one speed hard disk, that is, 2 GB hdds or 4 GB hdds.

Note:You can combine horizontal scaling and Vertical Scaling to optimize the connection scheme. The following are some principles to be followed:
· A maximum of four drive-Side Loop Pairs)
· A maximum of 8 exp expansion cabinets can be found in a drive loop pair.
· A ds4800 can connect up to 16 exp expansion cabinets
· Drive loop pair (loop pair) #1 drive loop pair (loop pair) #2 combination can have up to 8 exp expansion cabinets
· Drive loop pairs (loop pair) #3 drive loop pairs (loop pair #4 combination, up to 8 exp expansion cabinets allowed
· Drive loop pair (loop pair) #1 drive loop pair (loop pair) #2 must work at the same rate (2 or 4 Gbps per loop)
· Drive loop pair (loop pair) #3 drive loop pair (loop pair) #4 must work at the same rate (2 or 4 Gbps per loop)

2. Two Methods for connecting to the IBM ds4800 storage expansion Cabinet

First, let's take a look at the examples of horizontal and vertical scaling. This example assumes that all drive channel groups and their drive loop pairs (drive loop pairs) work at the same rate. In-1, a ds4800 is equipped with eight exp710s and adopts horizontal scaling. data bandwidth of up to 800 mb/sec can be utilized by all drives in each drive loop pair. in this case, four expansion cabinets (each consisting of two exp710s and 28 drives) have a maximum bandwidth of 800 mb/sec.

Figure-1 Horizontal ds4800 scaling, four drive loop pairs, using exp710

Note:The exp710 expansion cabinet is currently working at 2 Gbps. When the 4 Gbps exp expansion cabinet is released, the data bandwidth of 800 mb/sec can be obtained.

Assume that an application or a group of applications requires 1,200 Mb/s data bandwidth. In the past ds4000 model, there were up to two drive loop pairs to distribute data. in this way, such bandwidth cannot be simply obtained, and it is difficult for other Luns to share the remaining bandwidth. if you use four drive loop pairs of ds4800, You can distribute the lun to the hard disks of all four drive loop pairs to balance the load, allow you to increase bandwidth to meet the most important applications. In addition, distributing this Lun across all four drive loop pairs (instead of two) can provide higher availability than other ds4000 models.

When the demand for private bandwidth (dedicated bandwidth) arises, the vertical expansion may better meet the customer's needs than the horizontal expansion. Place Luns on only one drive loop to ensure that these Luns are only affected by this particular drive loop. This means that Luns on the drive loop can obtain a dedicated bandwidth up to 800 mb/sec. Distributing Luns to all drive loops allows you to use a bandwidth up to 3,200 Mb/s, but these Luns must share the bandwidth with other Luns.

Figure-2 Portrait extension on ds4800 using 2 drive-Side Loop Pairs

In, you can see that only two drive loop pairs are used. The benefit of vertical scaling is that Luns is only created on drive loops to 1 and has a dedicated bandwidth of up to 800 mb/sec. You can still get full protection. For large Luns, vertical expansion also allows you to use different back-end bandwidth rates on two different drive loops. In this case, the drive loop pair #1 and drive loop pair #2 must work at the same rate, and the drive loop pair #3 and drive loop pair #4 must work at the same rate. This is because the ports of each drive loop pair are shared in the same drive Channel group on Controller A and controller B ). On a ds4800, it is possible to create two pairs of drive loop pairs working at different rates. For example, drive loop pair #1 and drive loop pair #2 work in 4 Gbps mode, drive loop pair #3 and drive loop pair #4 work in 2 Gbps mode. Although the working mode at different rates is not recommended in ds4800, it can be implemented. 1 Gbps connections are not supported in ds4800 expansion cabinet connections.