RecoverPoint and NL_SAS replicas on VNX

Hi there,

The question is a little unclear in respect of what your issue or concern may be. From a RecoverPoint perspective a replication mode change will not make any difference iassuming you may mean the impact to the journla and replica distribution. As long as your have suffcient numbers of drives to satisfy the throughput requirement for the journal and replica distribution requirement the type of disk/drive does not matter. Obviously the slower the drive the more drives required.

Regards,

Richard Forshaw

Principal Corporate Systems Engineer - RecoverPoint (EMEA)

Data Mobility Business Unit - Enterprise Storage Division

EMC2 Computer Systems (UK) Ltd

Anyone have any experience of using NL_SAS for replicas on VNX?

Response : Yes. In some cases, customers choose to use NL-SAS Drives for replication target to save on cost with SAS drives for journal space. As long as SAS drives used for Journal can match the writes happening on the source luns, we are good.

Would this impact the production LUNs as the IOPS from NL_SAS do not match the Production Pool which in my customers case contains SSD and SAS drives.

Response : Depends on various factors like replication mode (sync/async), response time, number of writes on production etc.

                     Async – will not have much issue but sync – may experience some delays in some situations with high writes on production side.

When you write

Do you enable FAST Cache for the NL_SAS replica Pool?

Response : In production, Fast cache will benefit if you are accessing same block of data frequently where as NL-SAS drives are used for storing data that is not frequently used.

                    Replica pool ..  If you are building true DR solution with hosts on remote site, enabling all the features to match production array will make more sense.

Is it true that FAST Cache is not used for the Production Pool LUNs as it contains SSD drives so  enabling for the NL_SAS replica pool would be OK?

Response : Fast cache is not used for the data (Luns/part of lun) residing on SSD drives. Rest of the data residing on other drives of same pool is eligible to use FAST cache.

Enabling or disabling fast cache on replica pool is something to determine based on your specific plans.

Would setting to RP to Async mode be recommended in this example.  Thanks in advance for any replies.

Response : Decision of Sync versus Async is based on various factors, Distance between the arrays, connectivity, response time, tolerance of application, count and type of drives used for journals etc.

You might want to have a look at RP best practices guide and VNX Fast cache white paper before configuring.

Ramesh Polepalli

Response : Yes. In some cases, customers choose to use NL-SAS Drives for replication target to save on cost with SAS drives for journal space. As long as SAS drives used for Journal can match the writes happening on the source luns, we are good. - This is not the case. The MB/s throughput overhead is greater than the source being x3 for the journal and x2 for the replica for normal 5 phase distribution.

Would this impact the production LUNs as the IOPS from NL_SAS do not match the Production Pool which in my customers case contains SSD and SAS drives. - Potentially, see below.

Response : Depends on various factors like replication mode (sync/async), response time, number of writes on production etc.

                     Async – will not have much issue but sync – may experience some delays in some situations with high writes on production side. - If distribution is not quick enough even after moving from 5 phase to 3 phase distribution, the lag will grow to a point that we pause replication for async and perform marking of the writes. For sync we start to regulate the host/application (slow down) and then switch to async and then mark.

When you write

Do you enable FAST Cache for the NL_SAS replica Pool?

Response : In production, Fast cache will benefit if you are accessing same block of data frequently where as NL-SAS drives are used for storing data that is not frequently used.

                    Replica pool ..  If you are building true DR solution with hosts on remote site, enabling all the features to match production array will make more sense.

Is it true that FAST Cache is not used for the Production Pool LUNs as it contains SSD drives so  enabling for the NL_SAS replica pool would be OK?

Response : Fast cache is not used for the data (Luns/part of lun) residing on SSD drives. Rest of the data residing on other drives of same pool is eligible to use FAST cache.

Enabling or disabling fast cache on replica pool is something to determine based on your specific plans.

Would setting to RP to Async mode be recommended in this example.  Thanks in advance for any replies.

Response : Decision of Sync versus Async is based on various factors, Distance between the arrays, connectivity, response time, tolerance of application, count and type of drives used for journals etc. - If the environment is sized correctly, ideally using the EMC BCSD sizing tool, then this should not be an issue.

You might want to have a look at RP best practices guide and VNX Fast cache white paper before configuring.

I guess my question was would using Async mode help in a situation where the NL_SAS target replicas don't match the IOPS of the production LUNs and would enabling FAST Cache for the replica pool help in any way.I guess the answer is no as the journal and replicas potentially need even more iops.  Unless you have loads of NL_SAS spindles then it's unlikley that you would get the IOPS so NL_SAS is a bad choice for RecoverPoint replicas. In this case the orginal design had many more spindles but the customer reduced the spindle count before final purchase for budget reasons. Thanks for your responses.