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RAID 5 vs RAID 10 - How much performance gain

This question has been asked in different ways before, most recently here:
RAID 5 vs RAID 10 in drive array for SQL Server Database   (is the  performance boost really huge with RAID 10?)


We are setting up a newSQL Server now with
2 36GB SCSI drives for the OS (mirrored - RAID 1)
4 72GB SCSI drives for Data and Applications  (RAID ????)
The server is a HP ProLiant DL380G4p High Performance Dual 3.4GHz 2GB RAM (we will most likely add RAM, at least 1 GB).  We can't add more drives, there are only 6 bays so the only way to increase capacity later would be to replace the drives with bigger ones.

We were planning to turn the 4 drives into a RAID 5 and then partition this drive into 2 logical drives.  But now I am hearing that for better performance we should use RAID 10?  

My main question is:  is the  performance boost really huge?  

We are a small company (about 100 computer users) with about 50 people accessing the SQL datatbases regularly.  We are expecting a big boost in performance by switching to this new server from a 6 year old server.  Three main SQL based applications on this server:
Microsoft Dynamics Solomon - heavily customized
Goldmine  (CRM package)
Attendance Enterprise (time management system with 4 time clocks, punches primarily early am and around 4 pm - batch processed)
Each of these databases are 2 - 4 GB in size and growing.
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2 Solutions
Scott PletcherSenior DBACommented:
The logs really should go on the RAID 1 (or 10) drives (if necessary even with the O/S already there).  Logs and RAID 5 is *not* a good mix.

Read performance is roughly the same for R5/R10.  The big difference is in write performance: every write to R5 *also* requires two reads.  This slows you down -- the tradeoff is that you get fuller use of your resources, since less [redundant] space is required to implement R5 than R10.

So, how big the performance boost is depends on how many / what % of writes are done.  If it's mostly writes, you'll see a big boost; if it's mostly reads, you'll see much less boost.

Rule of thumb is to use R10 if you have the resources.  R5 if you need to squeeze the most space out of the hardware.
langerkingAuthor Commented:
What is the best way to measure % of writes?  I have looked at these Performance monitor counters

1.  PhysicalDisk %Disk Time     this was very low all the time
2.  PhysicalDisk Avg. Disk  Bytes/Read     this was very fairly high = spikes to 80%+, but falling in between
3.  PhysicalDisk Avg. Disk  Bytes/Write     this was not as high as 2. = mostly below 40%, spiking higher occasionally

I have looked in SQL 2000 Enterprise Manager and not found any way to capture anything there
Racim BOUDJAKDJIDatabase Architect - Dba - Data ScientistCommented:
Avoiding R5 is alway a good idea if you can afford disk space...RAID5 is a heavy IO contention creator on write intensive system (disk life expectancy decreases on this kind of configuration) and may degrade perfomance on intensive batch read systems as they may create significant joining overhead at controller level.

to evaluate roughly what kind of usage is done by your system, set up a Performance Monitor at prodution time to monitor the following ratio:

Physical Disk: Avg ms per Write/Physical Disk: Avg ms per Read

It may give you an indication onto how your system is primarly used...THEN you can plan for a corresponding RAID conf..

Hope this helps...
langerkingAuthor Commented:
Thanks for your help!

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