An Oracle blog – Amardeep Sidhu

February 18, 2019

Understanding grid disks in Exadata

Filed under: Exadata — Sidhu @ 6:37 pm
Tags: , ,

Use of Exadata storage cells seems to be a very poorly understood concept. A lot of people have confusions about how exactly ASM makes uses of disks from storage cells. Many folks assume there is some sort of RAID configured in the storage layer whereas there is nothing like that. I will try to explain some of the concepts in this post.

Let’s take an example of an Exadata quarter rack that has 2 db and 3 storage nodes (node means a server here). Few things to note:

  • The space for binaries installation on db nodes comes from the local disks installed in db nodes (600GB * 4 (expandable to 8) configured in RAID5). In case you are using OVM, same disks are used for keeping configuration files, Virtual disks for VMs etc.
  • All of the ASM space comes from storage cells. The minimum configuration is 3 storage cells.

So let’s try to understand what makes a storage cell. There are 12 disks in each storage cell (latest X7 cells are coming with 10 TB disks). As I mentioned above that there are 3 storage cells in a minimum configuraiton. So we have a total of 36 disks. There is no RAID configured in the storage layer. All the redundancy is handled at ASM level. So to create a disk group:

  • First of all cell disks are created on each storage cell. 1 physical disk makes 1 cell disk. So a quarter rack has 36 cell disks.
  • To divide the space in various disk groups (by default only two disk groups are created : DATA & RECO; you can choose how much space to give to each of them) grid disks are created. grid disk is a partition on the cell disk. slice of a disk in other words. Slice from each cell disk must be part of both the disk groups. We can’t have something like say DATA has 18 disks out of 36 and the RECO has another 18. That is not supported. Let’s say you decide to allocate 5 TB to DATA grid disks and 4 TB to RECO grid disks (out of 10 TB on each disk, approx 9 TB is what you get as usable). So you will divide each cell disk into 2 parts – 5 TB and 4 TB and you would have 36 slices of 5 TB each and 36 slices of 4 TB each.
  • DATA disk group will be created using the 36 5 TB slices where grid disks from each storage cell constitute one failgroup.
  • Similarly RECO disk group will be created using the 36 4 TB slices.

What we have discussed above is a quarter rack scenario with High Capacity (HC) disks. There can be somewhat different configurations too:

  • Instead of HC disks, you can have the Extreme Flash (EF) configuration which uses flash cards in place of disks. Everything remains the same except the number. Instead of 12 HC disks there will be 8 flash cards.
  • With X3 I think, Oracle introduced an eighth rack configuration. In an eighth rack configuration db nodes come with half the cores (of quarter rack db nodes) and storage cells come with 6 disks in each of the cell. So here you would have only 18 disks in total. Everything else works in the same way.

Hope it clarified some of the doubts about grid disks.


December 26, 2018

dbca doesn’t list diskgroups

Filed under: Database,Exadata — Sidhu @ 9:01 pm
Tags: ,

This is an Exadata machine running GI version 18.3.0.0.180717 and DB version 12.1.0.2.180717. On one of the DB nodes while running dbca, it doesn’t list the diskgroups. it works fine on the other node.

I cheked the dbca trace and found that the kfod command was failing. I tried to run it manually and got the same error:

[oracle@exadb01 ~]$ /u01/app/18.0.0.0/grid/bin/kfod op=groups verbose=true
KFOD-00300: OCI error [-1] [OCI error] [Could not fetch details] [-105777048]

KFOD-00105: Could not open pfile 'init@.ora'
[oracle@exadb01 ~]$

I ran it with strace then:

[oracle@exadb01 ~]$ strace /u01/app/18.0.0.0/grid/bin/kfod op=groups verbose=true
execve("/u01/app/18.0.0.0/grid/bin/kfod", ["/u01/app/18.0.0.0/grid/bin/kfod", "op=groups", "verbose=true"], [/* 18 vars */]) = 0
brk(0) = 0x2641000
.
.
.
.
.
open("/u01/app/18.0.0.0/grid/dbs/ab_+ASM1.dat", O_RDONLY) = -1 EACCES (Permission denied)
geteuid() = 1003
open("/u01/app/18.0.0.0/grid/rdbms/mesg/kfodus.msb", O_RDONLY) = 13
fcntl(13, F_SETFD, FD_CLOEXEC) = 0
lseek(13, 0, SEEK_SET) = 0
read(13, "\25\23\"\1\23\3\t\t\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"…, 280) = 280
lseek(13, 512, SEEK_SET) = 512
read(13, "\352\3\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"…, 512) = 512
lseek(13, 1024, SEEK_SET) = 1024
read(13, ".\1=\1E\1M\1X\1\352\3\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"…, 512) = 512
lseek(13, 1536, SEEK_SET) = 1536
read(13, "\n\0d\0\0\0D\0e\0\1\0e\0f\0\1\0\230\0g\0\1\0\306\0h\0\2\0\325\0"…, 512) = 512
fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 3), …}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f43f85f2000
write(1, "KFOD-00300: OCI error [-1] [OCI "…, 78KFOD-00300: OCI error [-1] [OCI error] [Could not fetch details] [-132605848]
) = 78

The text in bold just before the kfod error caught my attention. When I checked actually oracle user wasn’t able to read the file. The permissions looked like this:

[root@exadb01 dbs]# ls -ltr
total 20
-rw-r--r-- 1 oragrid oinstall 3079 May 14 2015 init.ora
-rw-r--r-- 1 oragrid oinstall 587 Dec 12 15:33 initbackuppfile.ora
-rw-rw---- 1 oragrid asmadmin 1656 Dec 20 14:26 ab_+ASM1.dat
-rw-rw---- 1 oragrid oinstall 1544 Dec 20 14:26 hc_+APX1.dat
-rw-rw---- 1 oragrid oinstall 1544 Dec 21 16:57 hc_+ASM1.dat
[root@exadb01 dbs]#

Whereas on node2 they were like:

[oracle@exadb02 dbs]$ ls -ltr 
total 16
-rwxrwxrwx 1 oragrid oinstall 3079 Dec 12 14:52 init.ora
-rwxrwxrwx 1 oragrid oinstall 1544 Dec 21 16:57 hc_+ASM2.dat
-rw-rw---- 1 oragrid oinstall 1720 Dec 21 16:57 ab_+ASM2.dat
-rwxrwxrwx 1 oragrid oinstall 1544 Dec 21 16:57 hc_+APX2.dat
[oracle@exadb02 dbs]$

Since oracle user isn’t member of asmadmin group, it is not able to read the mentioned file. Changing the owner to oragrid:oinstall fixed the issue.

November 21, 2018

New web based OEDA for Exadata

Filed under: Exadata — Sidhu @ 2:47 pm
Tags: ,

It started with an xls sheet (that was called dbm configurator) . Then OEDA (Oracle Exadata Deployment Assistant) was introduced that was a Java based GUI tool to enter all the information needed to configure an Exadata machine. Now with the latest patch released in Oct, OEDA has changed again; to become a web based tool. It is deployed on WebLogic and comes with some new features as well. SuperCluster deployments will continue to use the Java based OEDA tool.  The new interface has support for Exadata, ZDLRA and ExaCC. It is backward compatible and can import the XMLs generated by older versions of OEDA. Some of the new features include the ability to configure single instance homes, create more than 2 diskgroups, create more than 1 database homes and databases, allow ILOMs to have a different subnet etc.

To configure the OEDA application you need to unzip the contents and run the installWls script with -p switch (that mentions the port). It will deploy the application on WebLogic and give you the URL to access the OEDA. The interface is similar to the older version. Just that it runs in a browser and there are some new features added. MOS note 2460104.1 and the Exadata documentation has more details:

Using Oracle Exadata Deployment Assistant

 

 

November 6, 2017

Presenting at Cloud day event of North India Chapter of AIOUG

Filed under: General — Sidhu @ 5:17 pm
Tags: , ,

I will be presenting a session titled “An 18 pointers guide to setting up an Exadata machine” at Cloud Day being organized by North India chapter of AIOUG. Vivek Sharma is doing multiple sessions on various cloud and performance related topics. You can register for the event here

https://www.meraevents.com/event/aioug-nic-cloud-day 

 

November 5, 2017

ksplice kernel updates and Exadata patching

Filed under: Exadata — Sidhu @ 11:02 pm
Tags: , ,

If you have installed some one off ksplice fix for kernel on Exadata, remember to uninstall it before you do a kernel upgrade  eg regular Exadata patching. As such fixes are kernel version specific so they may not work with the newer version of the kernel. 

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