Hi
I have one Engine, one node.
Fresh install of oVirt 3.4 on new CentOS 6.5.
Engine holds ISO_DOMAIN, created automatically during setup.
The ISO_DOMAIN exists under Default -> Storage. When trying to attach it, it is visible in web interface a few seconds as "locked", then disappears.
Log says:
    ERROR [org.ovirt.engine.core.bll.storage.NFSStorageHelper] (org.ovirt.thread.pool-6-thread-24) [5a5288b3] The connection with details ctmgm0.certitrade.net:/ct/isos failed because of error code 477 and error message is: problem while trying to mount target (thanks for that error message... )
And a bit down:
    ERROR [org.ovirt.engine.core.bll.storage.AttachStorageDomainToPoolCommand] (org.ovirt.thread.pool-6-thread-27) [43f2f913] Command org.ovirt.engine.core.bll.storage.AttachStorageDomainToPoolCommand throw Vdc Bll exception. With error message VdcBLLException: org.ovirt.engine.core.vdsbroker.irsbroker.IRSErrorException: IRSGenericException: IRSErrorException: Failed to AttachStorageDomainVDS, error = Storage domain does not exist: ('0f6485ab-0301-4989-a59a-56efcd447ba0',), code = 358 (Failed with error StorageDomainDoesNotExist and code 358)

I can, however, mount the ISO_DOMAIN manually, it has correct permissions and a directory structure obviously created by oVirt (see below).
There is no problem adding nfs storage from the node.
iptables is off, no firewalld, selinux is permissive.

ISO_DOMAIN mounted on engine ("mount -t nfs 172.19.1.10:/ct/isos/ /mnt/tmp/")
ls -l /mnt/
totalt 4
drwxr-xr-x. 3 vdsm kvm 4096 10 jun 19.18 tmp

ls -l /mnt/tmp/0f6485ab-0301-4989-a59a-56efcd447ba0/images/
totalt 4
drwxr-xr-x. 2 vdsm kvm 4096 10 jun 19.19 11111111-1111-1111-1111-111111111111

I have read many posts about this problem, seems to be a common one, but no solution found.

Complete log from one try:
2014-06-11 15:48:23,513 INFO  [org.ovirt.engine.core.bll.storage.AttachStorageDomainToPoolCommand] (org.ovirt.thread.pool-6-thread-28) [7b977e41] Running command: AttachStorageDomainToPoolCommand internal: false. Entities affected :  ID: 0f6485ab-0301-4989-a59a-56efcd447ba0 Type: Storage
2014-06-11 15:48:23,525 INFO  [org.ovirt.engine.core.bll.storage.ConnectStorageToVdsCommand] (org.ovirt.thread.pool-6-thread-23) [795f995f] Running command: ConnectStorageToVdsCommand internal: true. Entities affected :  ID: aaa00000-0000-0000-0000-123456789aaa Type: System
2014-06-11 15:48:23,533 INFO  [org.ovirt.engine.core.vdsbroker.vdsbroker.ConnectStorageServerVDSCommand] (org.ovirt.thread.pool-6-thread-23) [795f995f] START, ConnectStorageServerVDSCommand(HostName = ExtTest, HostId = 1947b88f-b02e-4acf-bb30-1d92de626b45, storagePoolId = 00000000-0000-0000-0000-000000000000, storageType = NFS, connectionList = [{ id: 53c268c3-5b04-4d42-bfa3-58d31c982a5d, connection: ctmgm0.certitrade.net:/ct/isos, iqn: null, vfsType: null, mountOptions: null, nfsVersion: null, nfsRetrans: null, nfsTimeo: null };]), log id: 5107b953
2014-06-11 15:48:23,803 INFO  [org.ovirt.engine.core.dal.dbbroker.auditloghandling.AuditLogDirector] (org.ovirt.thread.pool-6-thread-23) [795f995f] Correlation ID: null, Call Stack: null, Custom Event ID: -1, Message: Failed to connect Host ExtTest to the Storage Domains ISO_DOMAIN.
2014-06-11 15:48:23,805 INFO  [org.ovirt.engine.core.vdsbroker.vdsbroker.ConnectStorageServerVDSCommand] (org.ovirt.thread.pool-6-thread-23) [795f995f] FINISH, ConnectStorageServerVDSCommand, return: {53c268c3-5b04-4d42-bfa3-58d31c982a5d=477}, log id: 5107b953
2014-06-11 15:48:23,808 INFO  [org.ovirt.engine.core.dal.dbbroker.auditloghandling.AuditLogDirector] (org.ovirt.thread.pool-6-thread-23) [795f995f] Correlation ID: null, Call Stack: null, Custom Event ID: -1, Message: The error message for connection ctmgm0.certitrade.net:/ct/isos returned by VDSM was: Problem while trying to mount target
2014-06-11 15:48:23,810 ERROR [org.ovirt.engine.core.bll.storage.NFSStorageHelper] (org.ovirt.thread.pool-6-thread-23) [795f995f] The connection with details ctmgm0.certitrade.net:/ct/isos failed because of error code 477 and error message is: problem while trying to mount target
2014-06-11 15:48:23,814 ERROR [org.ovirt.engine.core.bll.storage.ConnectStorageToVdsCommand] (org.ovirt.thread.pool-6-thread-23) [795f995f] Transaction rolled-back for command: org.ovirt.engine.core.bll.storage.ConnectStorageToVdsCommand.
2014-06-11 15:48:23,816 INFO  [org.ovirt.engine.core.vdsbroker.irsbroker.AttachStorageDomainVDSCommand] (org.ovirt.thread.pool-6-thread-28) [7b977e41] START, AttachStorageDomainVDSCommand( storagePoolId = 00000002-0002-0002-0002-00000000011b, ignoreFailoverLimit = false, storageDomainId = 0f6485ab-0301-4989-a59a-56efcd447ba0), log id: a2cca1b
2014-06-11 15:48:24,515 ERROR [org.ovirt.engine.core.vdsbroker.irsbroker.AttachStorageDomainVDSCommand] (org.ovirt.thread.pool-6-thread-28) [7b977e41] Failed in AttachStorageDomainVDS method
2014-06-11 15:48:24,547 ERROR [org.ovirt.engine.core.vdsbroker.irsbroker.IrsBrokerCommand] (org.ovirt.thread.pool-6-thread-28) [7b977e41] IrsBroker::Failed::AttachStorageDomainVDS due to: IRSErrorException: IRSGenericException: IRSErrorException: Failed to AttachStorageDomainVDS, error = Storage domain does not exist: ('0f6485ab-0301-4989-a59a-56efcd447ba0',), code = 358
2014-06-11 15:48:24,555 INFO  [org.ovirt.engine.core.vdsbroker.irsbroker.AttachStorageDomainVDSCommand] (org.ovirt.thread.pool-6-thread-28) [7b977e41] FINISH, AttachStorageDomainVDSCommand, log id: a2cca1b
2014-06-11 15:48:24,556 ERROR [org.ovirt.engine.core.bll.storage.AttachStorageDomainToPoolCommand] (org.ovirt.thread.pool-6-thread-28) [7b977e41] Command org.ovirt.engine.core.bll.storage.AttachStorageDomainToPoolCommand throw Vdc Bll exception. With error message VdcBLLException: org.ovirt.engine.core.vdsbroker.irsbroker.IRSErrorException: IRSGenericException: IRSErrorException: Failed to AttachStorageDomainVDS, error = Storage domain does not exist: ('0f6485ab-0301-4989-a59a-56efcd447ba0',), code = 358 (Failed with error StorageDomainDoesNotExist and code 358)
2014-06-11 15:48:24,559 INFO  [org.ovirt.engine.core.bll.storage.AttachStorageDomainToPoolCommand] (org.ovirt.thread.pool-6-thread-28) [7b977e41] Command [id=bff69195-7d00-4e18-bf5b-705be8d7210f]: Compensating NEW_ENTITY_ID of org.ovirt.engine.core.common.businessentities.StoragePoolIsoMap; snapshot: storagePoolId = 00000002-0002-0002-0002-00000000011b, storageId = 0f6485ab-0301-4989-a59a-56efcd447ba0.
2014-06-11 15:48:24,580 INFO  [org.ovirt.engine.core.dal.dbbroker.auditloghandling.AuditLogDirector] (org.ovirt.thread.pool-6-thread-28) [7b977e41] Correlation ID: 7b977e41, Job ID: fafb4906-a9dd-41fb-b17f-833d831e953e, Call Stack: null, Custom Event ID: -1, Message: Failed to attach Storage Domain ISO_DOMAIN to Data Center Default. (User: admin)

Regards
Peter Haraldson