EMC Storage Product Knowledge Sharing

I have been posting article related to CLARiiON recently. Lets talk about DMX Series. It is the most popular storage array from EMC. To manage DMX we have tool called ECC ( EMC Control Center, SMC and SYMCLI). Let me first explain what is gatekeeper and what is use?
To perform software operations on the Symmetrix, we use the low level SCSI command. To send SCSI commands to the Symmetrix, we need to open a device. We refer to the device we open as a gatekeeper. Symmetrix gatekeepers provide communication paths into the Symmetrix for external software monitoring and/or controlling the Symmetrix. There is nothing special about a gatekeeper, any host visible device can be used for this purpose. We do not actually write any data on this device, nor do we read any date from this device. It is simply a SCSI target for our special low level SCSI commands. We do perform I/O to these devices and this can interfere with applications using the same device. This is why we always configure small devices (NO data is actually stored) and map them to hosts to be used as "gatekeepers". Solutions Enabler will consider any device with 10 cylinders or less to be the preferred gatekeeper device.

Now you must have understood what is gatekeeper devices. Let me explain more about uses like how many gatekeeper you want to present host so there will be no performance impact.

A general recommendation for the number of gatekeepers for a single host with few applications running is 8. However, a common rule of thumb is a minimum of 6. For a host on which many applications running, 16 is recommended. A gatekeeper should not be mapped/masked to more than one host.
Granular Recommendation (for Solutions Enabler) :
It is hard to recommend an exact number of gatekeepers required for a single host. The number of gatekeeper's required depends on the specific host's configuration and role. This is because it directly relates to performance, therefore it is a subjective number. The following is a recommendation based upon a number of variables pertaining to that specific host. At least 2 gatekeepers for simple Solutions Enabler commands and 1 additional gatekeeper for each daemon or EMC Control Center Agent running on the host.
Granular Recommendation (for Control Center) :
• Two gatekeepers are required when the Storage Agent for Symmetrix is installed on the host, and two (total of four) additional gatekeepers are required when you use Symmetrix Configure commands to manage the Symmetrix system. Each Symmetrix system needs only two Symmetrix agents. The agents need to be installed on separate hosts. This is to provide for
failover when the primary agent goes down for maintenance (or failure).
• Common Mapping Agent and host agents do not require a gatekeeper.
• Note: SYMCLI scripts should not use gatekeepers assigned to ControlCenter; they should have their own.

Gatekeepers are typically 6 cylinders or 2888 KB in Size. All gatekeeper type devices should be protected by either RAID-1 or RAID-S.
Hope this will help you in deciding number of gatekeeper to assign the host.Because it is matter of performance.