November 22, 2002 at 9:48 am
I want to setup a new sql server as follows:
drive C: 2 mirrored 72 GB drives (for OS, trans logs)
drive D: 3 RAID-5 72 GB drives (for live database)
I was just told that the box has only one (1) array contoller. With this hardware config should I just go for one big RAID-5 drive with C and D partitions or does my original idea still have any value?
TIA,
Bill
November 22, 2002 at 10:26 am
You cannot install the OS to a RAID other than mirror from what I recall, I know you cannot use RAID 5 for sure.
November 22, 2002 at 12:03 pm
Antares is right about the OS.
Even with one channel I would build it as outlined. You won't gain as much, but the I/O activity Logs vs. Data tends to be very different. They will conflict if you were to setup say a single 5 drive raid5(lets say you have another drive for the OS)
Logs tend to be fairly sequential concentrated writes, Data is random all over.
KlK, MCSE
KlK
November 22, 2002 at 3:51 pm
Why can't you install OS to a RAID 5. The RAID is controlled by the card and so irrelevant to the OS. I thought!
I would go for RAID10 rather than RAID 5, if your system is a OLTP system then you will get better peformance, if you have a warehouse then your load will definitley benefit from RAID 10. Only if you need the extra space I would use RAID 5 but then the performance difference is big.
Simon Sabin
Co-author of SQL Server 2000 XML Distilled
http://www.amazon.co.uk/exec/obidos/ASIN/1904347088
Simon Sabin
SQL Server MVP
http://sqlblogcasts.com/blogs/simons
November 25, 2002 at 3:45 am
Antares686, where did you get info re RAID5.
We put OS on RAID5 (2 logical drives (C: for OS, D: for SQL)!
Far away is close at hand in the images of elsewhere.
Anon.
November 25, 2002 at 5:33 am
Guess my information is outdated, this was the case for older servers at one time, got to looking and see the new controllers should work fine. However, as I was looking around I found this in relation to Widnows 2000 that may help a bit on the decision.
http://support.microsoft.com/default.aspx?scid=kb;en-us;329707
December 3, 2002 at 7:36 pm
As long as you have hardware raid so the device looks like a single drive to the OS, you can install anything anywhere. The restriction about installing the OS on a non RAID device applies only when windows software is providing the RAID service. If you think about it, it makes sense because the OS has to be loaded before it can piece together scattered bits of files. If the bits are scattered, the BIOS isn't smart enough to find the boot info. Thus the hardware "smartens up" the BIOS so it can do it's deal.
Just be aware that with 3 devices, you lose 1/3 of the capacity. RAID 5 always loses ones of the physical devices you put behind it. You would be better off with 6 smaller drives instead of 3 larger drives. your capacity would be higher (only 1/6th of space lost) and your response marginally better provided there are 6 physically paths to allow simultaneous access to all drives.
December 3, 2002 at 7:43 pm
Bill, what type of box are you buying? How many drive bays?
K. Brian Kelley
http://www.truthsolutions.com/
Author: Start to Finish Guide to SQL Server Performance Monitoring
http://www.netimpress.com/shop/product.asp?ProductID=NI-SQL1
K. Brian Kelley
@kbriankelley
December 4, 2002 at 11:09 am
quote:
You would be better off with 6 smaller drives instead of 3 larger drives. your capacity would be higher (only 1/6th of space lost) and your response marginally better provided there are 6 physically paths to allow simultaneous access to all drives.
End quote
I both agree and disagree with this. 6 smaller drives over 3 larger drives is infinately better, but the performance gain would be substantial, not marginal. At 2X the available IO paths, and 2X the drive heads and platters, disk performance will more than double, especially under a heavy load.
Here's some examples from my archive....
These measurments were from Perfmon for drive thouroughput on my own Sql Server while importing 2.0 GB files. I am sorry to say I do not have actual numbers for any other than striped parity sets, and these were using 64KB block sizes. I probably should have recorded the measurments the numbers represent, but at the time I was interested in comparisons, using the same scale on all of them, so was not too worried in what the transfers/sec were, just the gain / loss between the setups.
1 Drive 3,045
2 Drives striped 15,087
4 Drives Striped 38,096
6 Drives striped 69,483
December 4, 2002 at 2:04 pm
But my concern for the setup is the single array controller. If it does not support multiple channels then you get the IO from one drive array set at a time synchronous on the drives in the array. If supports multiple channels then they are going down the right path, as each array set on a seperate channel will have a seperate IO stream for synchronous processing. Once you run out of channels thou you need to divy up the drives into arrays together.
December 4, 2002 at 2:19 pm
I simply assumed multiple channels, good catch Antares686, and excellent point.
December 4, 2002 at 3:18 pm
quote:
I both agree and disagree with this. 6 smaller drives over 3 larger drives is infinately better, but the performance gain would be substantial, not marginal.
This is the real point behind RAID anyway: multiple simultaneous paths to data. Too many folks look at RAID and don't see any farther beyond that. I don't deal with the actual hardware (other than this keyboard I can actually touch) but am quite aware of it. Vendors and evaluators needs to make it clear that the $999 model doesn't have the same multi-channel, simultaneous access and battery backup as the $2,999 model. ya they're both RAID 5 but ......
Also, many folks don't realize that RAID 5 ALWAYS costs one of the physical disks, regardless of size. With reliability factors today and relatively low incremental costs, It's probably not too big a deal. however, I think one can easily be suckered into something less that what was imagined.
December 5, 2002 at 9:52 am
If your raid controller supports it, and you have another available slot, why not go 6 drives in a RAID 10 (RAID 0+1) format? You'll end up with the same amout of logical disk space from what you suggest, and the performance will be much better than a RAID 5 array.
Too many people think RAID and think only RAID 5, RAID 0 + 1 is worth the little extra dough, especially for an OLTP DB.
quote:
I want to setup a new sql server as follows:drive C: 2 mirrored 72 GB drives (for OS, trans logs)
drive D: 3 RAID-5 72 GB drives (for live database)
I was just told that the box has only one (1) array contoller. With this hardware config should I just go for one big RAID-5 drive with C and D partitions or does my original idea still have any value?
TIA,
Bill
December 5, 2002 at 2:59 pm
I am still trying to figure how this coversation went to 6 drives when he states
2-72GB drives in RAID0
3-72GB drives in RAID5
Barring the fact I let my Hardware information get behind I only count 5 drives.
Based on everything you stated as long as the card will support 2 channels then putting each array on it's own channel then your setup is fine (1 controller as stated). If however the controller does not support multiple channels then do a single RAID 5 of all 5 drives (you even gain 72GB) this way you get simultaneous writes across all drives and no blocking on the array caused by a single channel single controller as you will have with the other layout. Cut and dry those are your 2 options to get maximum performance and complete redundancy. Sure if supports you could setup a RAID10 of 4-72GB drives with data and logs on that drive and a single 72GB drive for OS but then no redundancy on OS drive.
Other than that, try to invest into more hardware on a better box taking the recommendations presented here. Personally I would try to have OS to itself, logs to themselves, data to themselves and place tempdb to itself ultimately and aim for RAID5 minimum or RAID10 better on all but OS which I would do a mirrored drive.
Edited by - antares686 on 12/05/2002 3:01:42 PM
December 5, 2002 at 3:46 pm
Oh, come on Antares686, you've heard of scope creep, well this is thread creep.
LMAO...
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