Dell PowerConnect 5548 User Guide - Page 586

Limitations The following limitations exist: • All iSCSI connections receive the relevant QoS, regardless of whether they are being monitored or not. If, for example, a feature was disabled for some period and was enabled again, it is possible that there are iSCSI TCP connections that were established during this period of time. These cannot be monitored, because all relevant information was already passed at the beginning of the session. But these unidentified sessions will still be assigned to iSCSI QoS. • The maximum number of iSCSI TCP connections, which is also the default setting, is 1K. This can be changed after reset. • The number of iSCSI connections affects other system features. iSCSI-aware, DHCP Snooping, and ACL rules all use the TCAM system resource. If the number of iSCSI connections has been increased, the other application rules (DHCP Snooping or ACL) can be removed after reset. • If the target uses redirect messages upon the initiator request, and, as a result, the initiator opens a connection to a different target, the new target must be configured as part of the general configuration. • Only iSCSI flows to targets that use the iSCSI well-known port or other explicit user-defined configuration are assigned QoS. • The aging configuration works for each connection. The mechanism checks connection activities in a group of 28 TCP iSCSI connections, within the aging time. In the worst case, when the maximum number of 1K TCP connections are monitored and are not terminated gracefully, the mechanism causes inaccuracy, namely, the last 28 TCP iSCSI connections are aged out after (1K/28)*aging-time. • In general, the greater the number of ungracefully terminated iSCSI TCP connections, the greater the inaccuracy is. Not all iSCSI TCP connections are monitored for aging at the same time. Sessions, whose associated TCP connections are not being currently monitored, will show unchanged aging time. • Encryption (Ipsec) must not be applied on iSCSI traffic, otherwise a QoS profile will not be assigned to iSCSI. • iSCSI optimization does not work with IP fragmented frames. 586 Dell PowerConnect 55xx Systems User Guide