In order to connect to the same target with multiple initiators at the same time, a cluster filesystem has to be used. Otherwise, the data may become corrupted. Here are some SAN cluster filesystems: 

MelioFS:
http://www.sanbolic.com/melio.htm
IBM:
http://www-306.ibm.com/software/tivoli/products/sanergy/
http://www.ibm.qassociates.co.uk/storage-software-totalstorage-san-filesystem.htm
SGI:
http://www.sgi.com/products/storage/tech/file_systems.html
PolyServe:
http://www.polyserve.com
DataPlow SFS:
http://www.dataplow.com

Alternately, you may use MetaSAN software (http://www.tiger-technology.com/metasan/), which is cross-platform Storage Area Network (SAN) management software.

SAN file system solutions are very expensive. The easiest way to share the data on an iSCSI target is to create a network share and get clients to connect to the network share and not directly to the target.
If the clients have read only permissions on the target and need to access recent data (written from a single host only), they can log out and log in a new session in the initiator in order to see recent data.