January 24, 2013 at 7:14 pm
hi,
I am a developer and given dba responiblities by default. I have 3 sql servers that are in virtualized environments, 2 servers on one host server , 1 server on another host server , both host servers also have multiple guest servers other than just the sql servers. Performance varies from good to dead. While a great deal of query performance tuning can be done, one server is for an old third party application so my hands are tied there.
I am wondering what part virtualization or disk configuration contributes to bad performance?
I asked our Networking team about the disk configuration for the sql servers, ie what type RAID drive for the different drives (C,E etc..., I was told the host server is on a RAID6 but because sql server is on windows, there is no raid drive - I don't understand this because everything I am reading talks about putting logs and data files on RAID5, RAID10...etc Where does RAID6 fall on the scale of good to bad? Am I to assume because the host server is a RAID6, my C, E & F drives are also RAID6? In reading, seems RAID6 is good for recovery from disk failures but that it costs you in IO performance. Does anybody use RAID6 for sql servers?
Thank you,
KJ
January 24, 2013 at 8:11 pm
Raid 6 is just like Raid 5 with the addition of another parity bit. From a disk perspective there is no penalty for reads but you do generate overhead when writing due to the parity calculations which isnt ideal for an OLTP workload if thats what you have.
That being said you want to look at your hypervisor and see how its performing in all aspects not just disk before you dig into the disk subsystem. Ensuring your hypervisor is healthy is important before fixing one of its guest...
January 24, 2013 at 8:40 pm
two of the servers are OLTP, the third is used 70% for reporting but is just synomyns created from tables on one of the other OLTP servers.
January 25, 2013 at 1:55 am
Is this a VMWare ESX farm or some other hypervisor?
Which version of the hypervisor are you using?
Are the virtual machines disks all virtual disk files or are you using Raw Device Mappings?
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"Ya can't make an omelette without breaking just a few eggs" 😉
January 29, 2013 at 10:42 am
This is VMWare ESX version 4.1 I believe. I asked once if the sql had fixed resources so
i'm going to assume the disks are all virtual disk files. One of the servers has log and
data on the same drive, I don't know if it is worth seperating to an "F" drive when E and
F are essentially the same drive. In the monitoring we are doing I see alot of writelog
waits.
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