Oracle DB's on SAN

[groener]

I'm a newbie to being a SAN admin. I have a very small SAN to start with. IBM DS4800 (4GB total cache) with 2 drawers.

16x146GB 15k 4gb FC
16x300GB 10K 2gb FC

The fastest stuff (146GB) I'm going to use to house two separate Oracle DB's. Their I/O is not through the roof. One has the potential for some decent I/O down the road, because it is an email database. I'm attempting to migrate off of old SSA direct-attached disk scheme.

My question is "should I create one RAID 5 array out of that drawer and make 2 luns for the DB's" or "should I make two even sized RAID 5 arrays out of that drawer". I'll take as many opinions as I can get!!

Thanks,

Chad Groen
Good Samaritan Society

 

[steinweo]

Hi,

There is no easy answer, but there are 2 major schools depending if you want to have different workload on same physical disks. If not, cause you want to be sure that one workload won't interfer with the other (or as few as possible) go for one RAID group per application/host. Otherwise, you can have less RAID groups.

But, a common practice is to have RAID5 group with 3D + 1P or 7D + 1P.

Regards, Olivier.

 

[sgabriel62]

Your question should also have input from Oracle DBAs - I think they will offer two equal sized RAID5 - but of the overhead is not bad - why dont you introduce two RAID 0/1 with a hot spare?

 

[groener]

Raid 0/1

Yeah, I've been mulling that over too, but my boss would like to see us not waste so much disk space. 2 RAID 5 arrays is still wasting another in parity. RAID0+1 would burn up even more disk. These two drawers are all I've got to replace about 14 full drawers of SSA disk. (unfortunately)

 

[groener]

Anyone using RAID 50?

Would this be a workable option that would only use one more disk worth of parity (two RAID 5 arrays + RAID 0)?

Then, I would have my two Oracle DB LUN's across that....Hopefully not having to worry about any performance issues.

 

[gyuzik]

I agree with sgabriel62, you need some information from your DBA's.

1) Will everything be control files (database files), will you be storing logs (archive, redo, accounting)
2) How much space is requried for each.

Each RAID level has there own pro/cons... i.e. databases are random access, logs are sequential.

Idealy you will want to build them the fastest datastore possible with the DS4800. I use a DS4300 with multiple RAID 5 than have the OS stripe accoss them, this allows my to have all the spindles spinning at the same rate verses have a few "hot" disks.

Keep in mind that SNIA recommends you keep your disk count to 8 or less, if you have a 15 disk array and suffer a disk failure... it would take a very long time for your to rebuild the array during that time and could suffer a double-disk-failure.

 

[groener]

Thanks for the input!

I didn't know it was common practice to keep the RAID5 arrays under 8 disks. I did have a long rebuild on a DS4100 come to think of it (full drawer RAID5) I think I'll not worry about the amount of spindles and go with 3-5 disk RAID5's and one hot spare. That way I have one more array set aside for another high-performance DB.

Didn't even know the SNIA existed! (Shows how much of a newbie I am)

Thanks again to all....I'll take more suggestions if anyone wants to chime in.