Archieve setting for Sales Documents

Dear Experts,

My question is related to the following forums -

http://scn.sap.com/thread/301774

http://scn.sap.com/thread/301776

http://scn.sap.com/thread/1961452

In SARA, for archieving docs. such as object "SD_VBAK", under "Customizing - Archiving Object-Specific Customizing - Technical Settings", found that our previous colleague set "A2" for the "Content Repository" of section "Place file in Storage System" as below -

When archieving the sales docs., these docs. could be arvhieved but the relevant storage job was canceled as below -

Date       Time     Message text                                                                                                                     Message class Message no. Message type

17.09.2015 18:19:32   Job started                                                                                                                        00           516          S

17.09.2015 18:19:32   Step 001 started (program RSARCH_STORE_FILE, variant , user ID HITD1234)         00           550          S

17.09.2015 18:19:32   Archive file 000035-001SD_VBAK is being processed                                                   BA           165          S

17.09.2015 18:19:32   Content repository A2 does not exist                                                                             CMS          002          S

17.09.2015 18:19:32   Archive file 000035-001SD_VBAK cannot be stored                                                       BA           149          E

17.09.2015 18:19:32   Job cancelled after system exception ERROR_MESSAGE                                             00           564          A

From the above link, it should be due to miss setup in OAC0 and also found that there is no relevant "A2" Content Repository in our OAC0,  just found similar setting for the Cont.Rep.ID "A2" in OAC3, e.g.

Object Type & Doc. Type = ARCHIVE

L = X

Cont.Rep.ID = A2

Link = TOA01

Now, my question is to ask whether it is necessary to set the "A2" (or other value) under the "Customizing - Archiving Object-Specific Customizing - Technical Settings" of SARA archieving object (e.g. SD_VBAK) ? or just leave it blank ? If required to set the "A2" (or other value), should we have to complete all settings in the OAC0 & OAC3 ?

For your ref., in our another development client, we had ever tested to remove the "A2" & leave it blank, and changed to another logical file name "ARCHIVE_DATA_FILE2" (instead of the "ARCHIVE_DATA_FILE") under the "Customizing - Archiving Object-Specific Customizing - Technical Settings" and then archieving the sales docs. could also be completed and the sales docs. could also be retrieved in "Information System - Archive Explorer". Just could not find the "StorageSyst' button in the initial screen of SARA for Object "SD_VBAK" as below -

Many Thanks

KH Fong