Checking Flash Cache Mode in Exadata Cloud

By | February 28, 2019

While looking at an exachk report for an Exadata rack running in Oracle Cloud Infrastructure, I saw an interesting finding:

Since this is an Oracle cloud environment, we don't have any access to view the storage servers - they are managed and maintained by Oracle.  For several reasons, I believed this to be a false alert, but wanted to see if I could determine what the flashcachemode setting is.

On some flavors of Exadata cloud service, you have access to run exacli to perform limited commands similar to cellcli.  Unfortunately, we either aren't running that service, or we don't have the passwords available to us.

I took a look in the V$CELL_CONFIG view inside a database running on the cluster, and was able to get the information I needed out of the view using this script:

set lines 150
set pages 100
col hostname for a30
col flashcachemode for a50
       Xmlquery('/cli-output/context[@cell]' passing Xmltype(confval)
       content) AS hostname,
       Xmlquery('/cli-output/cell/flashCacheMode' passing Xmltype(confval)
       content) AS flashcachemode
FROM   v$cell_config
WHERE  conftype = 'CELL'

When I ran the command, here was my output:

HOSTNAME                                 FLASHCACHEMODE
--------------------------------------   --------------------------------------------------
<context cell="phx301102exdcl07"/>	 <flashCacheMode>WriteBack</flashCacheMode>
<context cell="phx301102exdcl12"/>	 <flashCacheMode>WriteBack</flashCacheMode>
<context cell="phx301102exdcl11"/>	 <flashCacheMode>WriteBack</flashCacheMode>
<context cell="phx301102exdcl10"/>	 <flashCacheMode>WriteBack</flashCacheMode>
<context cell="phx301102exdcl09"/>	 <flashCacheMode>WriteBack</flashCacheMode>
<context cell="phx301102exdcl08"/>	 <flashCacheMode>WriteBack</flashCacheMode>

And there you have it - all of the cells are in WriteBack mode. Just to see what it would look like, I reconfigured the flashcache in the Enkitec lab on one storage server for WriteThrough, and got the following result:

HOSTNAME                       FLASHCACHEMODE
-------------------------      --------------------------------------------------
<context cell="enkx4cel01"/>   <flashCacheMode>WriteBack</flashCacheMode>
<context cell="enkx4cel04"/>   <flashCacheMode>WriteBack</flashCacheMode>
<context cell="enkx4cel03"/>   <flashCacheMode>WriteThrough</flashCacheMode>
<context cell="enkx4cel02"/>   <flashCacheMode>WriteBack</flashCacheMode>

There are several other things that you can see from the V$CELL_CONFIG view, including celldisks, griddisks, and open alerts.

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