今天在家折騰自己的小實驗室，把自己NAS上的一個目錄用NFS掛載到一套11g RAC的實驗環境中。
當我在備份數據庫到NAS上時，發現一個奇怪的問題，同樣的目錄下，默認backup 備份集的情況，備份是成功的，但如果使用backup as copy備份則會報錯，現象如下：
RMAN> backup datafile 6 format '/public/backup/oradb23/dbs_d_jingyu.bak';
Starting backup at 25-MAR-17
using channel ORA_DISK_1
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00006 name=+DATA/jyzhao/datafile/dbs_d_jingyu.268.937515173
channel ORA_DISK_1: starting piece 1 at 25-MAR-17
channel ORA_DISK_1: finished piece 1 at 25-MAR-17
piece handle=/public/backup/oradb23/dbs_d_jingyu.bak tag=TAG20170325T210550 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:07
Finished backup at 25-MAR-17
Starting Control File and SPFILE Autobackup at 25-MAR-17
piece handle=/public/backup/oradb23/c-2520969382-20170325-01 comment=NONE
Finished Control File and SPFILE Autobackup at 25-MAR-17
RMAN> backup as copy datafile 6 format '/public/backup/oradb23/%u.dbf';
Starting backup at 25-MAR-17
using channel ORA_DISK_1
channel ORA_DISK_1: starting datafile copy
input datafile file number=00006 name=+DATA/jyzhao/datafile/dbs_d_jingyu.268.937515173
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03009: failure of backup command on ORA_DISK_1 channel at 03/25/2017 21:07:30
ORA-19504: failed to create file "/public/backup/oradb23/0vs0200h.dbf"
ORA-27054: NFS file system where the file is created or resides is not mounted with correct options
Additional information: 3
Additional information: 12
RMAN>
看backup as copy的報錯明顯是告訴我們無法在/public/backup/oradb23/目錄下創建文件，但目錄肯定有寫權限，不然備份集備份也一樣不會成功。
使用oerr簡單先查看該錯誤號的說明：
[oracle@oradb23 ~]$ oerr ora 27504
27504, 00000, "IPC error creating OSD context"
// *Cause: This is an operating system/cluster interconnect error.
// *Action: Check the value of errno and contact Oracle Support Services.
也沒有太多有價值的內容。
進而查看MOS，最終找到下面這篇文檔，
Mount Options for Oracle files for RAC databases and Clusterware when used with NFS on NAS devices (文檔 ID 359515.1)
RAC including RACone and single instance RAC
In the table below
Binaries is the shared mount points where the Oracle Home and CRS_HOME is installed.
Datafiles includes Online Logs, Controlfile and Datafiles
nfsvers and vers are identical on those OS platforms that has nfsvers. The ver option is an alternative to the nfsvers option. It is included for compatibility with other operating systems
Please note that the mount options on each of the following cells are applicable only to those type of files listed in the column heading.
For RMAN backup sets, image copies, and Data Pump dump files, the "NOAC" mount option should not be specified - that is because RMAN and Data Pump do not check this option and specifying this can adversely affect performance.
Due to Unpublished bug 5856342, it is necessary to use the following init.ora parameter when using NAS with all versions of RAC on Linux (x86 & X86-64 platforms) until 10.2.0.4. This bug is fixed and included in 10.2.0.4 patchset.
filesystemio_options = DIRECTIO
大概意思是存儲數據文件的話，在mount時，還需要指定一些特定的選項：
--vi /etc/fstab
#192.168.1.196:/mnt/HD/HD_a2/Public /public nfs rw
192.168.1.196:/mnt/HD/HD_a2/Public /public nfs rw,bg,hard,nointr,rsize=32768,wsize=32768,tcp,actimeo=0,vers=3,timeo=600
第一行注釋的是之前我配置的NFS掛載，而實際如果要存放數據文件，則需要按照上面提到的MOS文檔進行配置，也就是第二行內容。
修改完重新掛載/public, 再次測試backup as copy，已經可以正常備份了。
RMAN> backup as copy datafile 6 format '/public/backup/oradb23/%u.dbf';
Starting backup at 25-MAR-17
using channel ORA_DISK_1
channel ORA_DISK_1: starting datafile copy
input datafile file number=00006 name=+DATA/jyzhao/datafile/dbs_d_jingyu.268.937515173
output file name=/public/backup/oradb23/17s022f8.dbf tag=TAG20170325T214928 RECID=16 STAMP=939592197
channel ORA_DISK_1: datafile copy complete, elapsed time: 00:00:35
Finished backup at 25-MAR-17
Starting Control File and SPFILE Autobackup at 25-MAR-17
piece handle=/public/backup/oradb23/c-2520969382-20170325-03 comment=NONE
Finished Control File and SPFILE Autobackup at 25-MAR-17
至此，就可以正常backup as copy到我的NAS設備中了。