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Autoraid performance problems with oracle

ALH
Occasional Advisor

Autoraid performance problems with oracle

We have a K580 with an array 12H (autoraid) with 12 18Gb HDD?s
On this array we have created an Oracle database with a total storage of 35 Gb. The database is spread over two LUNS of 23 Gb each with crossed primary / alternate SCSI controllers. The unallocated space would be about 14 Gb. After creating the database we saw that all the database files are written in RAID 5 and not in RAID 1. When we created it the RAID 0/1 space was a several 100 Mb?s.
Above is a test situation for the porting of one of our applications to HP-UX and Oracle. When we go in production the unallocated space for the autraid would be ? 70 Gb.
The question is now : is there a way to get de databasefiles default written in RAID 0/1 even as the RAID 0/1 space allocated is just a several 100 Mb?s and the write working set is in GB (logprint info)
Please tell what i must do to get a good performance from the start.

Cees Wielink
Netherlands
7 REPLIES
Maarten van Maanen
Regular Advisor

Re: Autoraid performance problems with oracle

The 12H will move files from Raid 5 to Raid 0/1 on the basis of them being requested. At the start (eq, restore) everything will be simply written to disk. When in use the 12H will re-allocate files and build up the Raid 0/1 space.
When we reconfigured our 12H and restored the data the initial raid 0/1 space started at 9Mb (from a previous 25000Mb). This has increased to 22000Mb at present. I have included the script I use to monitor this build-up.
This is what the 12H will do automatically and over which the user has no control. If you want the 12H to start out with a large Raid 0/1 space I suggest you give it something to do (start copying files, fill up the volumes, delete the files again) and you will see Raid 0/1 space grow automatically. Using Logprint you can monitor the Raid 5 to 1 reallocation info to see how it is doing.
Other than this, I know of no other way to 'force the 12H' to go to a specific state. This, in fact, is also what the 12H was designed for, to take that job out of the hands of the administrator. Something, I must admit, is/was not always to my liking.
eric watson
Advisor

Re: Autoraid performance problems with oracle

Hi
In general the AutoRAID manages the 0/1 space for you. You do not have any control over it. In general the more LUNs the better. Here is some additional info:


Optimizing Performance
Disk array performance is influenced by many factors, some host-related, some related to the configuration
of the disk array itself. Host-related disk array performance issues can typically be identified and corrected
using operating system utilities or third-party applications designed for this purpose.
The following list identifies some of the factors that directly influence disk array performance. Other
factors, such as a rebuild, can temporarily affect array performance.
+ Amount of available RAID 0/1 ? In most cases, the more RAID 0/1 space available, the better the
disk array performance. With enough RAID 0/1 space, the disk array can service all write I/Os from
RAID 0/1, thus allowing an optimum write working set. RAID 0/1 space can be increased by
increasing the amount of unallocated capacity on the disk array.
+ Enabling Active Hot Spare ? With Active Hot Spare enabled, the disk array can recover quickly from
a disk failure without the need for any action on your part. This maintains performance because while
the disk array is operating in non-redundant or critical mode, performance decreases. Active Hot Spare
provides an additional performance benefit because it is used as RAID 0/1 space until a disk fails.
+ Amount of cache DRAM ? Increasing the amount of cache DRAM can alleviate bottlenecks that may
form in the controller data path. This increases the rate at which the disk array can service host I/Os.
+ Proper disk module installation ? Installing the disk modules in the correct slots in the enclosure
distributes the disks across the internal SCSI busses and balances the I/O load properly. Disk modules
should be installed from left-to-right, top-to-bottom.
+ Keep the disk capacity small ? Having twelve disks with smaller capacities will improve the
performance as compared to having twelve disks with larger capacities.
Dragan Krnic
Frequent Advisor

Re: Autoraid performance problems with oracle

If you are really keen on performance, Cees, you should get rid of 12h. Buy 2 enclosures and simply mirror your 12 disks for netto 12*9=108GB. The AutoRAID will always stand in the way of performance.
Patrick Wallek
Honored Contributor

Re: Autoraid performance problems with oracle

Unfortunately with the AutoRaid devices there is not a way to explicitly define what uses Raid 0/1 and what uses Raid 5. The AutoRaid has some 'smarts' built in that causes it to automatically move data from Raid 5 to 0/1 or vice versa as it sees fit.

I have two AutoRaid 12H's and I have never really been pleased with their performance. It is partially because of the Raid 0/1 and Raid 5 issue and partially because the SCSI bus to the system is FWD/DIFF and the internal SCSI bus is SE.
Dragan Krnic
Frequent Advisor

Re: Autoraid performance problems with oracle

Get rid of RAID if you're serious about your database.

Re: Autoraid performance problems with oracle

You can force the autoraid 12h to go into Raid 0/1 configuration by allocating the total lun space less or equal to half the space. In this case the autoraid will work exclusively in Raid 0/1. Hope this will help.
Mark van Silfhout
Trusted Contributor

Re: Autoraid performance problems with oracle

Cees,

Indeed, since it is AUTOraid you do not have control about RAID levels (with an FC-60 or XP, you would have). If you need everything in RAID 0/1 than do not assign more than:
12*18GB minus 1* 18Gb (for hot spare) and take 50% of this= 99Gb to LUNS.
Creating 2+ LUNS in the volumegroup and striping across the LUNS can speed up I/O's.

At this moment your database is in RAID 5, but the autoraid will balance itself (when there's none/few I/O traffic), your database might be in RAID 0/1 in a few days time. The autoraid will try to keep the least accessed data in RAID 5 to get full performance and the most frequent accessed data (which will be in 0/1).

Regards,

Mark