What is Gate Keeper Device

Kalyan, the following is from Primus solution emc180055:

What are Gatekeepers?
As the size of Symmetrix arrays increase, to effectively monitor and manage an array, more and more data must be exchanged between the ControlCenter Agents responsible for the Symmetrix arrays (Symmetrix / SDM) and the Symmetrix arrays themselves.  Gatekeepers are normal Symmetrix devices used to facilitate this data exchange.

Where do I need Gatekeepers?
Gatekeepers should be assigned per attached management host.  A management host is any host running a copy of Solutions Enabler intended to be used for Symmetrix monitoring and management.  Since Solutions Enabler does more than just monitor Symmetrix Arrays, not all hosts with Solutions Enabler will need gatekeepers assigned.

Per management host, how many Gatekeepers do I need?
The minimum number of Gatekeepers supported by EMC are 5.  When less than 5 Gatekeepers are available to a management host, both SMC and the ControlCenter console will generate alerts stating that fewer than 5 gatekeepers are present. Six (6) Gatekeepers is sufficient to satisfy the communication requirements for Symmetrix Management Console (SMC) and ControlCenter’s Symmetrix Management and SDM agents.  When planning the storage management environment where ControlCenter and SMC components reside together on the same host, only six (6) gatekeepers are required per Symmetrix management host.  Assigning additional gatekeepers does not provide any significant benefit.

From the point-of-view of the Symmetrix, how many Gatekeepers do I need to create?
First, count the number of hosts that will be used to actively manage the Symmetrix.  This is typically a very small number.  Take this number, and multiply it by 6.  That is the total number of Gatekeepers that should be created on the Symmetrix.  For example, in an environment with 4 management hosts, a total of 24 Gatekeepers should be created.  Each unique Gatekeeper should only be assigned to one FA port, and masked to only one host HBA.  This ensures Gatekeepers are not shared across multiple hosts, which could reduce the management performance.

How do I create Gatekeeper devices?
Create Gatekeeper devices like any other device, but keep the size to 2880 KB.  See the ControlCenter Online Help for instructions.  Once created, map the devices to the appropriate Symmetrix front-end port, then mask the devices to the appropriate host HBAs.

How do Gatekeepers assist in communicating with Symmetrix arrays?
Communication with Symmetrix arrays occurs by sending syscalls to the array along the same channels used for normal storage I/O.  For Open Systems hosts, this means we send monitoring and management commands over SCSI protocol (SCSI pass-through commands) to Symmetrix devices visible to that host.  As long as devices (LUNs) from an array are visible to a host, a Symmetrix Agent installed on that host can actively manage that Symmetrix array.

There can be performance issues, however, if we are using the same devices for both I/O (read-write) and management.  Sending one type of command can cause the other to block until the outstanding commands are completed.  To get around this problem, you can present special devices to the host called Gatekeepers.

Gatekeepers are normal Symmetrix devices (of any type), that have a very small size.  Most Gatekeeper devices are below 3 MB in size.  This makes it very difficult to accidentally perform I/O operations to the device (since there is practically no usable space on the device), ensuring the device is only used for monitoring and management commands.  ControlCenter, through Solutions Enabler, automatically recognizes these devices as Gatekeepers, and will prefer these devices when performing management functions.

Each Gatekeeper can handle a certain amount of traffic before it becomes locked.  Once outstanding commands are completed, the Gatekeeper will become unlocked and new commands can be processed.  In situations where many commands are being sent simultaneously (like in the case of Symmetrix and SDM Agents), multiple Gatekeepers are needed to ensure all commands are processed in a speedy manner.

From a management host, how can I check the number of assigned Gatekeepers?
The easiest way to check on the number of Gatekeepers visible from a Symmetrix Agent host is to log on to the host and use the "syminq" command:

C:\Program Files\EMC\SYMCLI\bin>syminq

           Device                   Product                   Device
-------------------------- --------------------------- ---------------------
Name                Type   Vendor    ID           Rev  Ser Num      Cap (KB)
-------------------------- --------------------------- ---------------------
\.\PHYSICALDRIVE0          SEAGATE   ST3146807LC  DS09 N/A               N/A
\.\PHYSICALDRIVE1          DGC       RAID 5       0219 16000001      5242880
\.\PHYSICALDRIVE2          DGC       RAID 5       0219 15000001      5242880
\.\PHYSICALDRIVE3          DGC       RAID 5       0219 13000001      5242880
\.\PHYSICALDRIVE4          DGC       RAID 5       0219 2C000029      2131968
\.\PHYSICALDRIVE5          DGC       RAID 10      0219 3D0000C5       563200
\.\PHYSICALDRIVE6          EMC       SYMMETRIX    5670 7900000000      23040
\.\PHYSICALDRIVE7          EMC       SYMMETRIX    5670 7900000000      23040
\.\PHYSICALDRIVE8  GK      EMC       SYMMETRIX    5670 7900037000       2880
\.\PHYSICALDRIVE9  GK      EMC       SYMMETRIX    5670 7900038000       2880
\.\PHYSICALDRIVE10 R1      EMC       SYMMETRIX    5670 7900039000    1048320
\.\PHYSICALDRIVE11 R1      EMC       SYMMETRIX    5670 790003A000    1048320
\.\PHYSICALDRIVE12 R2      EMC       SYMMETRIX    5670 790003E000    1048320
\.\PHYSICALDRIVE13 R2      EMC       SYMMETRIX    5670 790003F000    1048320
\.\PHYSICALDRIVE14 BCV     EMC       SYMMETRIX    5670 7900040000    1048320
\.\PHYSICALDRIVE15 BCV     EMC       SYMMETRIX    5670 7900041000    1048320
\.\PHYSICALDRIVE16 BCV     EMC       SYMMETRIX    5670 7900042000    1048320
\.\PHYSICALDRIVE17         EMC       SYMMETRIX    5670 7900045000    1048320
\.\PHYSICALDRIVE18         EMC       SYMMETRIX    5670 7900046000    1048320
\.\PHYSICALDRIVE19         EMC       SYMMETRIX    5670 7900047000    1048320
\.\PHYSICALDRIVE20         EMC       SYMMETRIX    5670 790004A000    1048320
\.\PHYSICALDRIVE21         EMC       SYMMETRIX    5670 790004B000    1048320
\.\PHYSICALDRIVE22         EMC       SYMMETRIX    5670 790004C000    1048320
\.\PHYSICALDRIVE23 GK      EMC       SYMMETRIX    5670 79000CD000       2880
\.\PHYSICALDRIVE24 GK      EMC       SYMMETRIX    5670 79000CE000       2880
\.\PHYSICALDRIVE25         DGC       RAID 5       0219 E800000C     10485760

The above output was from Solutions Enabler 6.0.  In the output:

• The Type column will let you know if Solutions Enabler considers a particular device to be a Gatekeeper (GK).
• In the "Ser Num" column, the first 2 digits of the number are actually the last two digits of the Symmetrix serial number.  This lets you know which devices are from which Symmetrix arrays. 
• The next 5 digits of the "Ser Num" column are the Symmetrix device number.
• Notice the Gatekeeper (GK) devices in the output all have a size of 2880 KB

From this output, you can accurately see how many unique Gatekeeper devices are visible from this host.  You will want to do this on each Symmetrix Agent / SDM Agent host to ensure that the Agent can see the correct Symmetrix arrays, and that there are enough Gatekeepers assigned.  Also be sure to not expose the same Gatekeeper devices to more than one Agent host, as they will compete with each other to communicate with the Symmetrix.

Hello, Symmetrix gatekeepers are usually small volumes with about 3MB in size.

They are used by the Solutions Enabler for communications purposes with the array (configurations, query, TimeFinder scripting, etc)

Hope this info works for you!

Erika G.

Hey Thanks all...Now I have brief understanding about Gate Keeper Device...

Regards,

Kalyan Guturi.

Thanks for the brief information 'MicMac', it helped me understand in detail.