# How is choosen the master or primary slot of the cluster? **URL:** \ **Category:** Technical Forums\ **Tags:** virtualization, management, vcmp, guest, ltm, application-delivery\ **Created:** [December 1, 2014, 3:35pm UTC](https://community.f5.com/t/how-is-choosen-the-master-or-primary-slot-of-the-cluster/2691 "2014-12-01T15:35:00Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Angel\_Lopez\_116](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Angel\_Lopez\_116](https://community.f5.com/u/Angel_Lopez_116)\ **Post date:** [December 1, 2014, 3:35pm UTC](https://community.f5.com/t/how-is-choosen-the-master-or-primary-slot-of-the-cluster/2691/1 "2014-12-01T15:35:00Z")
Hi there, I’d like to know how the cluster master slot is choosen? Is there any rule or algorithm to choose the primary slot on boot? I’m wondering why my Viprion has decided this configuration after booting: **On the vCMP host:** ```tcl ----------------------------------------- Sys::Cluster: default ----------------------------------------- Address 192.168.16.32/21 Availability available State enabled Reason Cluster Enabled Primary Slot ID 1 Primary Selection Time 11/27/14 09:03:31 ---------------------------------------------------------------------------------------------------------------------- | Sys::Cluster Members | ID Address Availability State Licensed HA Clusterd Reason ---------------------------------------------------------------------------------------------------------------------- | 1 192.168.16.33 available enabled true active running Run | 2 192.168.16.34 available enabled true active running Run | 3 :: unknown disabled false unknown shutdown Slot powered off or empty, manually disabled | 4 :: unknown disabled false unknown shutdown Slot powered off or empty, manually disabled ``` **On the guest:** ```tcl ----------------------------------------- Sys::Cluster: default ----------------------------------------- Address 192.168.16.55/21 Availability available State enabled Reason Cluster Enabled Primary Slot ID 2 Primary Selection Time 11/27/14 09:06:27 ---------------------------------------------------------------------------------- | Sys::Cluster Members | ID Address Availability State Licensed HA Clusterd Reason ---------------------------------------------------------------------------------- | 1 :: available enabled true active running Run | 2 :: available enabled true active running Run | 3 :: unknown enabled false unknown shutdown Slot powered off or empty | 4 :: unknown enabled false unknown shutdown Slot powered off or empty ``` I’d expect to see the guest active on slot 1 too, how is this? It doesn’t matter that the slot 1 is the active one for the host and slot 2 for the guest? ---
**Author:** ![Brad\_Parker\_139](https://avatars.discourse-cdn.com/v4/letter/b/b9e5f3/32.png) [@Brad\_Parker\_139](https://community.f5.com/u/Brad_Parker_139)\ **Post date:** [December 1, 2014, 3:51pm UTC](https://community.f5.com/t/how-is-choosen-the-master-or-primary-slot-of-the-cluster/2691/2 "2014-12-01T15:51:39Z")
It doesn’t matter which blade is chosen as the primary for either the vCMP host or vCMP guest. If you had more blades and more guests its entirely possible to have the primary of all of them be different. As to how that decision is made, I have not found documentation on that, though through observations it appears it generally chooses the first available slot but don’t quote me on that. It may choose the least busy, but I honestly couldn’t say for sure. ---
**Author:** ![Brad\_Parker](https://avatars.discourse-cdn.com/v4/letter/b/a87d85/32.png) [@Brad\_Parker](https://community.f5.com/u/Brad_Parker)\ **Post date:** [December 1, 2014, 3:51pm UTC](https://community.f5.com/t/how-is-choosen-the-master-or-primary-slot-of-the-cluster/2691/3 "2014-12-01T15:51:39Z")
It doesn’t matter which blade is chosen as the primary for either the vCMP host or vCMP guest. If you had more blades and more guests its entirely possible to have the primary of all of them be different. As to how that decision is made, I have not found documentation on that, though through observations it appears it generally chooses the first available slot but don’t quote me on that. It may choose the least busy, but I honestly couldn’t say for sure. ---
**Author:** ![Nick\_T\_68319](https://avatars.discourse-cdn.com/v4/letter/n/91b2a8/32.png) [@Nick\_T\_68319](https://community.f5.com/u/Nick_T_68319)\ **Post date:** [December 1, 2014, 4:48pm UTC](https://community.f5.com/t/how-is-choosen-the-master-or-primary-slot-of-the-cluster/2691/4 "2014-12-01T16:48:09Z")
I’m not 100% sure, but I think it’s whatever blade boots up faster and gets it’s services running. On mine I noticed, if Slot1 is primary, then you reboot the chassis, the secondary blades reboot faster. So after the next reboot Slot2 will be primary. ---
**Author:** ![Angel\_Lopez\_116](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Angel\_Lopez\_116](https://community.f5.com/u/Angel_Lopez_116)\ **Post date:** [December 1, 2014, 7:36pm UTC](https://community.f5.com/t/how-is-choosen-the-master-or-primary-slot-of-the-cluster/2691/5 "2014-12-01T19:36:21Z")
So the primary role is just to set the source from which the system will be replicated to a new blade, right? It doesn’t have any other relevance. ---
**Author:** ![Angel\_Lopez\_116](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Angel\_Lopez\_116](https://community.f5.com/u/Angel_Lopez_116)\ **Post date:** [December 1, 2014, 7:36pm UTC](https://community.f5.com/t/how-is-choosen-the-master-or-primary-slot-of-the-cluster/2691/6 "2014-12-01T19:36:21Z")
So the primary role is just to set the source from which the system will be replicated to a new blade, right? It doesn’t have any other relevance. ---
**Author:** ![Angel\_Lopez\_116](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Angel\_Lopez\_116](https://community.f5.com/u/Angel_Lopez_116)\ **Post date:** [December 1, 2014, 7:36pm UTC](https://community.f5.com/t/how-is-choosen-the-master-or-primary-slot-of-the-cluster/2691/7 "2014-12-01T19:36:57Z")
I see… it seems that there’s no rule to decide who will be the master. ---
**Author:** ![Brad\_Parker\_139](https://avatars.discourse-cdn.com/v4/letter/b/b9e5f3/32.png) [@Brad\_Parker\_139](https://community.f5.com/u/Brad_Parker_139)\ **Post date:** [December 2, 2014, 1:39am UTC](https://community.f5.com/t/how-is-choosen-the-master-or-primary-slot-of-the-cluster/2691/8 "2014-12-02T01:39:49Z")
“When the cluster initializes, one blade is determined to be the primary blade and all other blades are secondary blades. In addition to processing traffic like other blades, the primary blade is a management blade, which sets and maintains the configuration for the whole cluster.” [404 Page not found | BIG-IP Documentation](https://support.f5.com/kb/en-us/solutions/public/10000/700/sol10778.html?sr=29127145) ---
**Author:** ![Brad\_Parker](https://avatars.discourse-cdn.com/v4/letter/b/a87d85/32.png) [@Brad\_Parker](https://community.f5.com/u/Brad_Parker)\ **Post date:** [December 2, 2014, 1:39am UTC](https://community.f5.com/t/how-is-choosen-the-master-or-primary-slot-of-the-cluster/2691/9 "2014-12-02T01:39:49Z")
“When the cluster initializes, one blade is determined to be the primary blade and all other blades are secondary blades. In addition to processing traffic like other blades, the primary blade is a management blade, which sets and maintains the configuration for the whole cluster.” [404 Page not found | BIG-IP Documentation](https://support.f5.com/kb/en-us/solutions/public/10000/700/sol10778.html?sr=29127145)