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    <title>FCIP Tape Acceleration </title>
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<a name="wp1077154"> </a><h1 class="pTitle">
FCIP Tape Acceleration

</h1>
<a name="wp1152245"> </a><p class="pBody">
The FCIP write acceleration feature enables you to significantly improve application write performance 
when storage traffic is routed over wide area networks using FCIP. When FCIP write acceleration is 
enabled, WAN throughput is maximized by minimizing the impact of WAN latency for write operations. 
The write acceleration feature is disabled by default and must be enabled on both sides of the FCIP link. 

</p>
<a name="wp1077156"> </a><p class="pBody">
Tapes are storage devices that store and retrieve user data sequentially. Cisco MDS NX-OS provides both 
tape write and read acceleration. 

</p>
<a name="wp1077157"> </a><p class="pBody">
Applications that access tape drives normally have only one SCSI WRITE or READ operation 
outstanding to it. This single command process limits the benefit of the tape acceleration feature when 
using an FCIP tunnel over a long-distance WAN link. It impacts backup, restore, and restore performance 
because each SCSI WRITE or READ operation does not complete until the host receives a good status 
response from the tape drive. The FCIP tape acceleration feature helps solve this problem. It improves 
tape backup, archive, and restore operations by allowing faster data streaming between the host and tape 
drive over the WAN link. 

</p>
<a name="wp1077161"> </a><p class="pBody">
In an example of tape acceleration for write operations, the backup server inissues write operations to a 
drive in the tape library. Acting as a proxy for the remote tape drives, the local Cisco MDS switch proxies 
a transfer ready to signal the host to start sending data. After receiving all the data, the local Cisco MDS 
switch proxies the successful completion of the SCSI WRITE operation. This response allows the host 
to start the next SCSI WRITE operation. This proxy method results in more data being sent over the FCIP 
tunnel in the same time period compared to the time taken to send data without proxying. The proxy 
method improves the performance on WAN links.

</p>
<a name="wp1077168"> </a><p class="pBody">
At the tape end of the FCIP tunnel, another Cisco MDS switch buffers the command and data it has 
received. It then acts as a backup server to the tape drive by listening to a transfer ready from the tape 
drive before forwarding the data.

</p>
<a name="wp1077169"> </a><p class="pBodyAutonumNoRule">
<strong>Note	&nbsp;&nbsp;&nbsp;</strong> In some cases such as a quick link up/down event (FCIP link, Server/Tape Port link) in a tape library 
environment that exports Control LUN or a Medium Changer as LUN 0 and tape drives as other LUNs, 
tape acceleration may not detect the tape sessions and may not accelerate these sessions. You need to 
keep the FCIP link disabled for a couple of minutes before enabling the link. This does not apply to tape 
environments where the tape drives are either direct FC attached or exported as LUN 0.

</p>
<a name="wp1077170"> </a><p class="pBody">
The Cisco NX-OS provides reliable data delivery to the remote tape drives using TCP/IP over the WAN. 
It maintains write data integrity by allowing the WRITE FILEMARKS operation to complete end-to-end 
without proxying. The WRITE FILEMARKS operation signals the synchronization of the buffer data 
with the tape library data. While tape media errors are returned to backup servers for error handling, tape 
busy errors are retried automatically by the Cisco NX-OS software.

</p>
<a name="wp1077174"> </a><p class="pBody">
In an example of tape acceleration for read operations, the restore serverissues read operations to a drive 
in the tape library. During the restore process, the remote Cisco MDS switch at the tape end, in 
anticipation of more SCSI read operations from the host, sends out SCSI read operations on its own to 
the tape drive. The prefetched read data is cached at the local Cisco MDS switch. The local Cisco MDS 
switch on receiving SCSI read operations from the host, sends out the cached data. This method results 
in more data being sent over the FCIP tunnel in the same time period compared to the time taken to send 
data without read acceleration for tapes. This improves the performance for tape reads on WAN links.

</p>
<a name="wp1077181"> </a><p class="pBody">
The Cisco NX-OS provides reliable data delivery to the restore application using TCP/IP over the WAN. 
While tape media errors during the read operation are returned to the restore server for error handling, 
the Cisco NX-OS software recovers from any other errors. 

</p>
<a name="wp1077182"> </a><p class="pBodyAutonumNoRule">
<strong>Note	&nbsp;&nbsp;&nbsp;</strong> The FCIP tape acceleration feature is disabled by default and must be enabled on both sides of the FCIP 
link. If it is only enabled on one side of the FCIP tunnel, the tape acceleration feature is turned 
operationally off.

</p>
<a name="wp1077183"> </a><p class="pBodyAutonumRel">
<strong>Tip	&nbsp;&nbsp;&nbsp;</strong> FCIP tape acceleration does not work if the FCIP port is part of a PortChannel or if there are multiple 
paths between the initiator and the target port. Such a configuration might cause either SCSI discovery 
failure or broken write or read operations.

</p>
<a name="wp1077184"> </a><p class="pCaution">
<table border="0">
<tr>
<td>
<strong>Caution	&nbsp;&nbsp;&nbsp;</strong>
</td>
<td>
<p>When tape acceleration is enabled in an FCIP interface, a FICON VSAN cannot be enabled in that 
interface. Likewise, if an FCIP interface is up in a FICON VSAN, tape acceleration cannot be enabled 
on that interface.
</p>
</td>
</tr>
</table>

</p>
<a name="wp1077185"> </a><p class="pBodyAutonumNoRule">
<strong>Note	&nbsp;&nbsp;&nbsp;</strong> When you enable the tape acceleration feature for an FCIP tunnel, the tunnel is reinitialized and the write 
and read acceleration feature is also automatically enabled.

</p>
<a name="wp1077186"> </a><p class="pBody">
In tape acceleration for writes, after a certain amount of data has been buffered at the remote Cisco MDS 
switch, the write operations from the host are flow controlled by the local Cisco MDS switch by not 
proxying the Transfer Ready. On completion of a write operation when some data buffers are freed, the 
local Cisco MDS switch resumes the proxying. Likewise, in tape acceleration for reads, after a certain 
amount of data has been buffered at the local Cisco MDS switch, the read operations to the tape drive 
are flow controlled by the remote Cisco MDS switch by not issuing any further reads. On completion of 
a read operation, when some data buffers are freed, the remote Cisco MDS switch resumes issuing reads.

</p>
<a name="wp1077187"> </a><p class="pBody">
The default flow control buffering uses the <b class="cBold">automatic </b>option. This option takes the WAN latencies and 
the speed of the tape into account to provide optimum performance. You can also specify a flow control 
buffer size (the maximum buffer size is 12 MB).

</p>
<a name="wp1077188"> </a><p class="pBodyAutonumRel">
<strong>Tip	&nbsp;&nbsp;&nbsp;</strong> We recommend that you use the default option for flow-control buffering.

</p>
<a name="wp1077189"> </a><p class="pBodyAutonumRel">
<strong>Tip	&nbsp;&nbsp;&nbsp;</strong> Do not enable time-stamp control on an FCIP interface with tape acceleration configured.

</p>
<a name="wp1077190"> </a><p class="pBodyAutonumNoRule">
<strong>Note	&nbsp;&nbsp;&nbsp;</strong> If one end of the FCIP tunnel is running Cisco MDS SAN-OS Release 3.0(1) or later and NX-OS Release 
4.x, and the other end is running Cisco MDS SAN-OS Release 2.x, and tape acceleration is enabled, then 
the FCIP tunnel will run only tape write acceleration, not tape-read acceleration.

</p>
<a name="wp1077191"> </a><p class="pBodyAutonumNoRule">
<strong>Note	&nbsp;&nbsp;&nbsp;</strong> In Cisco MDS NX-OS Release 4.2(1), the FCIP Tape Acceleration feature is not supported on FCIP 
back-to-back connectivity  between  MDS switches.

</p>
<a name="wp1077192"> </a><h2 class="pHeading2">
Tape Library LUN Mapping for FCIP Tape Acceleration
</h2>
<a name="wp1077193"> </a><p class="pBody">
If a tape library provides logical unit (LU) mapping and FCIP tape acceleration is enabled, you must 
assign a unique LU number (LUN) to each physical tape drive accessible through a target port. 

</p>
<a name="wp1077210"> </a><p class="pBody">
For the mappings described in <a href="cfcip20.html#wp1077218">Table&#160;2-1</a> and <a href="cfcip20.html#wp1077261">Table&#160;2-2</a>, Host 1 has access to Drive 1 and Drive 2, and 
Host 2 has access to Drive 3 and Drive 4.

</p>
<a name="wp1077214"> </a><p class="pBody">
<a href="cfcip20.html#wp1077218">Table&#160;2-1</a> describes correct tape library LUN mapping.

</p>
<a name="wp1152304"> </a><p class="pBodyRelative">
</p><div>
<table border="2" cellpadding="2" id="wp1077218table1077215">
  <caption><a name="wp1077218"> </a><div class="pTableTitle">
Table&#160;2-1	Correct LUN Mapping Example with Single Host Access

</div>
</caption>
  <tr bgcolor="#CCCCCC" align="left" valign="middle">    <th><a name="wp1077224"> </a><p class="pCellHeading">
Host

</p>
</th>
    <th><a name="wp1077226"> </a><p class="pCellHeading">
LUN Mapping

</p>
</th>
    <th><a name="wp1077228"> </a><p class="pCellHeading">
Drive

</p>
</th>
</tr>
  <tr align="left" valign="top">    <td colspan="1" rowspan="2"><a name="wp1077230"> </a><p class="pBody">
Host 1

</p>
</td>
    <td><a name="wp1077232"> </a><p class="pBody">
LUN 1

</p>
</td>
    <td><a name="wp1077234"> </a><p class="pBody">
Drive 1

</p>
</td>
</tr>
  <tr align="left" valign="top">    <td><a name="wp1077238"> </a><p class="pBody">
LUN 2

</p>
</td>
    <td><a name="wp1077240"> </a><p class="pBody">
Drive 2

</p>
</td>
</tr>
  <tr align="left" valign="top">    <td colspan="1" rowspan="2"><a name="wp1077242"> </a><p class="pBody">
Host 2

</p>
</td>
    <td><a name="wp1077244"> </a><p class="pBody">
LUN 3

</p>
</td>
    <td><a name="wp1077246"> </a><p class="pBody">
Drive 3

</p>
</td>
</tr>
  <tr align="left" valign="top">    <td><a name="wp1077250"> </a><p class="pBody">
LUN 4

</p>
</td>
    <td><a name="wp1077252"> </a><p class="pBody">
Drive 4

</p>
</td>
</tr>
</table>
</div>
<p class="pBodyRelative">
</p>
<a name="wp1077257"> </a><p class="pBody">
<a href="cfcip20.html#wp1077261">Table&#160;2-2</a> describes incorrect tape library LUN mapping.

</p>
<a name="wp1152309"> </a><p class="pBodyRelative">
</p><div>
<table border="2" cellpadding="2" id="wp1077261table1077258">
  <caption><a name="wp1077261"> </a><div class="pTableTitle">
Table&#160;2-2	Incorrect LUN Mapping Example with Single Hosts Access

</div>
</caption>
  <tr bgcolor="#CCCCCC" align="left" valign="middle">    <th><a name="wp1077267"> </a><p class="pCellHeading">
Host

</p>
</th>
    <th><a name="wp1077269"> </a><p class="pCellHeading">
LUN Mapping

</p>
</th>
    <th><a name="wp1077271"> </a><p class="pCellHeading">
Drive

</p>
</th>
</tr>
  <tr align="left" valign="top">    <td colspan="1" rowspan="2"><a name="wp1077273"> </a><p class="pBody">
Host 1

</p>
</td>
    <td><a name="wp1077275"> </a><p class="pBody">
LUN 1

</p>
</td>
    <td><a name="wp1077277"> </a><p class="pBody">
Drive 1

</p>
</td>
</tr>
  <tr align="left" valign="top">    <td><a name="wp1077281"> </a><p class="pBody">
LUN 2

</p>
</td>
    <td><a name="wp1077283"> </a><p class="pBody">
Drive 2

</p>
</td>
</tr>
  <tr align="left" valign="top">    <td colspan="1" rowspan="2"><a name="wp1077285"> </a><p class="pBody">
Host 2

</p>
</td>
    <td><a name="wp1077287"> </a><p class="pBody">
LUN 1

</p>
</td>
    <td><a name="wp1077289"> </a><p class="pBody">
Drive 3

</p>
</td>
</tr>
  <tr align="left" valign="top">    <td><a name="wp1077293"> </a><p class="pBody">
LUN 2

</p>
</td>
    <td><a name="wp1077295"> </a><p class="pBody">
Drive 4

</p>
</td>
</tr>
</table>
</div>
<p class="pBodyRelative"> 
</p>
<a name="wp1077297"> </a><p class="pBody">
Another example setup is when a tape drive is shared by multiple hosts through a single tape port. For 
instance, Host 1 has access to Drive1 and Drive2, and Host 2 has access to Drive 2, Drive 3, and Drive 
4. A correct LUN mapping configuration for such a setup is shown in <a href="cfcip20.html#wp1077304">Table&#160;2-3</a>.

</p>
<a name="wp1152314"> </a><p class="pBodyRelative">
</p><div>
<table border="2" cellpadding="2" id="wp1077304table1077301">
  <caption><a name="wp1077304"> </a><div class="pTableTitle">
Table&#160;2-3	Correct LUN Mapping Example with Multiple Host Access

</div>
</caption>
  <tr bgcolor="#CCCCCC" align="left" valign="middle">    <th><a name="wp1077310"> </a><p class="pCellHeading">
Host

</p>
</th>
    <th><a name="wp1077312"> </a><p class="pCellHeading">
LUN Mapping

</p>
</th>
    <th><a name="wp1077314"> </a><p class="pCellHeading">
Drive

</p>
</th>
</tr>
  <tr align="left" valign="top">    <td colspan="1" rowspan="2"><a name="wp1077316"> </a><p class="pBody">
Host 1

</p>
</td>
    <td><a name="wp1077318"> </a><p class="pBody">
LUN 1

</p>
</td>
    <td><a name="wp1077320"> </a><p class="pBody">
Drive 1

</p>
</td>
</tr>
  <tr align="left" valign="top">    <td><a name="wp1077324"> </a><p class="pBody">
LUN 2

</p>
</td>
    <td><a name="wp1077326"> </a><p class="pBody">
Drive 2

</p>
</td>
</tr>
  <tr align="left" valign="top">    <td colspan="1" rowspan="3"><a name="wp1077328"> </a><p class="pBody">
Host 2

</p>
</td>
    <td><a name="wp1077330"> </a><p class="pBody">
LUN 2

</p>
</td>
    <td><a name="wp1077332"> </a><p class="pBody">
Drive 2

</p>
</td>
</tr>
  <tr align="left" valign="top">    <td><a name="wp1077336"> </a><p class="pBody">
LUN 3

</p>
</td>
    <td><a name="wp1077338"> </a><p class="pBody">
Drive 3

</p>
</td>
</tr>
  <tr align="left" valign="top">    <td><a name="wp1077342"> </a><p class="pBody">
LUN 4

</p>
</td>
    <td><a name="wp1077345"> </a><p class="pBody">
Drive 4

</p>
</td>
</tr>
</table>
</div>
<p class="pBodyRelative">
</p>
<hr /><br><p class="pBody">Copyright 2010-2013, Cisco Systems, Inc. All rights reserved.</p> 

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