March 14, 2006 at 8:18 am
Ok, taking a survey. I'm spec'ing out an HP Proliant DL360 G4p. It max's out at 4 internal drives. So, I'm looking at four HP 72GB 15,000 RPM SCSI U320 drives. Now, vote on a RAID config.
1) OS, Swap file, Program Files, Transaction Logs on 2 drive mirror.
Database data files on 2 drive mirror.
OR
2) Everything on a 4 drive RAID10 (2 drive stripped pairs with another mirrored set). Should have strong write and read capabilities.
Keep in mind that I expect my DB workload to be 90% random read/write, 10% seqential access. In fact, the 10% sequential would likely be due to power user queries and DBA tasks.
Please vote. I've never actually worked on RAID10 so I have no personal experience to go on.
Thanks in advance.
Ryan
March 14, 2006 at 8:34 am
Ryan
I suppose it depends how much of your read/write is write. Transaction logs are written to sequentially so if you have a fair amount of write activity then you should consider placing the logs on one RAID1 array and everything else on the other. I think it's more important to separate files in this way than it is to get whatever benefits RAID10 gives you. If you choose this option then you should logically partition the OS/data files array so that growing data files don't stop your OS from working and so that you can reformat your OS volume without losing your data, should you ever need to.
John
March 14, 2006 at 9:39 am
You're right, TLOG writes are sequential so I should alter my statement. 90% of my activity will be very small singleton reads/writes. There will be very little activity with large batch statements of any kind. There will be LOTS of:
INSERT INTO dbo.Table (col1, col2, col3, col4)
VALUES (val1, val2, val3, val4)
Of the 90% singleton statements, 90% will be of the INSERT variety above. 10% would be simple selects.
The last remaining total 10% will be sizable read, update, DBCC batches.
So far I have one vote for:
-OS, prog files, swap, mdf's ON RAID1
-TLogs on separate RAID1
Thanks
Ryan
March 15, 2006 at 3:07 am
Ryan,
How much activity are you expecting on this server? How many user connections? You're asking advice on RAID config for performance, but you tend to stability is also important. That only leads to 2 sets of raid 1.
Hth
JP
March 15, 2006 at 6:28 am
It's very hard for me to say what the traffic volume will be. This will be a very small ecommerce site with a very specific product. Based on your statement, I'm assumming you want to recommend RAID5...is that the case?
With the server limited to 4 drives, the only way I could increase "stability" (I assume you're referring to fault tolerance or redundancy) would be to build a 3 drive RAID5 with an online spare (not used unless there is a failure). This is the only way I know of to allow 2 drives to fail at the same time - which the mirrors may also allow, depending on if we are talking about one failure per mirror or not.
Anyway, RAID5 does not excel at small writes, which would be the bulk majority of the IO operations for this box. Also, the OS, progs, swap file, data files and t-logs would all be competing for time on the same set.
Check out RAID5 on the following link:
http://www.ecs.umass.edu/ece/koren/architecture/Raid/basicRAID.html
Ryan
March 15, 2006 at 6:38 am
Ryan,
You're right about the diff processes competing for the same disk when you would use RAID 5. I think that creating 2 arrays (RAID1) is a better choice. If, you would lose 2 disk at the same time, you will always be able to reconstruct your database to the exact point in time of the crash. (assuming that you ave a good db backup on some kind of media and the full recovery model set on your DB).
Another interesting issue you haven't mentioned about is the numer bof IO controllers wou will be using. Are you going to use 2 controllers ? If so, try to get these redundant. I don't know exactly if that can be done, but in that case you could afford to lose one...
JP
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