07-22-2007 03:56 PM
07-26-2007 10:46 AM
07-27-2007 02:39 AM
07-30-2007 09:35 PM
Your logic is correct.
In order to prevent an SRL bottleneck, SRL performance should be proportional to the sum of all volumes you intend on replicating. This can be calculated as IOPS or MB/s.
The difference (which has been pointed out) between the SRL and data volumes is the read / write pattern. The SRL is read and written sequentially. Under optimal circumstances it is only written too. However, if your network suffers an outage; upon re-establishing connectivity VVR will read from the SRL in order to synchronise the secondary with the primary. The amount that needs to be read is subject to the duration of the network outage and volume of writes accumulated during the outage. We call this SRL readback.
Consequently, to cater for current performance and some level of readback it would be ideal to provision additional performance. For example, say a factor of 110% of the data volumes performance.
With respect to physical SRL layout there are three strategies available:
1. Dedicate disk spindles to the SRL
Benefit of this strategy is that performance is deterministic. Downside is when allocating disk with performance in mind it is inevitable that you will be left with spare capacity that can not be used elsewhere (for performance reasons).
2. Use the SAME approach.
Stripe and Mirror Everything so that data and SRL volumes share a portion of the disks available performance and capacity.
Benefit of this strategy is balanced performance and optimal capacity utilisation. Downside is you add risk by adopting a shared model since a striped disk layouts performance is only as good as its weakest link (i.e. hot spot). Having said that, if the upfront design is thorough and reporting / performance monitoring is ongoing the risk is manageable.
3. Use solid state disk
Benefit of this strategy is that performance is deterministic and capacity utilisation is optimal since solid state disks capacity and performance ratios are more in line with the SRL's capacity / performance mix. Downside is obviously expense and availability.
Unfortunately, there is no silver bullet nor do I believe in them. The strategy you adopt should be aligned with your projects objectives and systems posture (e.g. is the environment risk averse? If so, use dedicated disks or solid state. If the environment is cost conscious use the SAME approach).
Hope this helps.
Message Edited by maral on 07-30-200709:40 PM