When considering the number of ranks, take into account the maximum disk operations per second per rank as shown in Table B-3.These are measured at 100% DDM Utilization with no cache benefit and with the average I/O being 4KB. Larger transfer sizes will reduce the number of operations per second.

Based on these values you can calculate how many host I/O per second each rank can handle at the recommended utilization of 40%. This is shown for workload read-write ratios of 70% read and 50% read in Table B-3.

Table B-3 Disk operations per second per RAID rank

RAID rank type

Disk ops/sec

Host I/O/sec

Host I/O/sec

 

 

 

 

(70% read)

(50% read)

 

 

 

 

 

RAID-5

15K RPM (7 + P)

1700

358

272

 

 

 

 

 

RAID-5

10K RPM (7 + P)

1100

232

176

 

 

 

 

 

RAID-5

15K RPM (6 + P + S)

1458

313

238

 

 

 

 

 

RAID-5

10K RPM (6 + P + S)

943

199

151

 

 

 

 

 

RAID-10

15K RPM (3 + 3 + 2S)

1275

392

340

 

 

 

 

 

RAID-10

10K RPM (3 + 3 + 2S)

825

254

220

 

 

 

 

 

RAID-10

15K RPM (4 + 4)

1700

523

453

 

 

 

 

 

RAID-10

15K RPM (4 + 4

1100

338

293

 

 

 

 

 

 

As can be seen in Table B-3,RAID-10 can support higher host I/O rates than RAID-5. However, you must balance this against the reduced effective capacity of a RAID-10 rank when compared to RAID-5.

Sharing ranks between iSeries and other servers

As a general guideline consider using separate extent pools for iSeries workload and other workloads. This will isolate the I/O for each server.

However, you may consider sharing ranks when the other servers’ workloads have a sustained low disk I/O rate compared to the iSeries I/O rate. Generally, iSeries has a relatively high I/O rate while that of other servers may be lower – often below one I/O per GB per second.

As an example, a Windows file server with a large data capacity may normally have a low I/O rate with less peaks and could be shared with iSeries ranks. However, SQL, DB or other application servers may show higher rates with peaks, and we recommend using separate ranks for these servers.

Unlike its predecessor the ESS, capacity used for logical units on the DS6000 can be reused without reformatting the entire array. Now, the decision to mix platforms on an array is only one of performance, since the disruption previously experienced on ESS to reformat the array no longer exists.

Connecting via SAN switches

When connecting DS6000 systems to iSeries via switches, you should plan that I/O traffic from multiple iSeries adapters can go through one port on a DS6000 and zone the switches accordingly. DS6000 host adapters can be shared between iSeries and other platforms.

356DS6000 Series: Concepts and Architecture

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IBM DS6000 Series manual Sharing ranks between iSeries and other servers, Connecting via SAN switches