October 31, 2017 at 8:41 am
Hi Steve,
You may get more feedback on this than you know what to do with. There are a lot of small shops out there like the one I work for that will have to squeeze all of the performance they can out of the Sql servers they have and then some. Over the years I've worn many hats and now I have the luxury of working with the infrastructure and tuning side of things. I've learned that SAN is nice but was never intended as a performance tool. It is a storage management tool. Local disk arrays will always out-perform a SAN. You just cannot escape physics.
Have a great day.
Richard
Richard L. Dawson
Microsoft Sql Server DBA/Data Architect
I can like a person. People are arrogant, ignorant, idiotic, irritating and mostly just plain annoying.
October 31, 2017 at 1:34 pm
Steve Jones - SSC Editor - Friday, October 27, 2017 11:02 AMmig28mx - Friday, October 27, 2017 9:16 AMHi Steve,
In my case, I started to work with db servers using Informix. It was used by our erp system in a hp autoraid. It worked very fine and in those times RAID 5 was the most preffered configuration besides RAID 0+1. Also in those times, to ensure the fastest search of data, the more disk plates spining and the more disk heads reading the data, it was the best recomendation.
I remmeeber that in the Informix User Group (IUG), one of the gurus send us a document where it claims that RAID 5 was the worst configuration for DB. In this configuration, if one drive fails, the spare disk will recover the data. But if a second drive in the array fail, then the whole array is down, as well as all the data. It was a shocking moment for me due to we were at RAID 5. To short the story, we changed our configuration to raid 0, that it is the recommended configuration for DB, and distributed the data trhough the disk.This was almost 20 years ago, and nowadays, using a SAN, I still distributed the data using different SAN disk drives in SQL and spliting index and data into different SAN disk drives. I perfectly know that a SAN disk may be composed by several physical disks and it ensures me that I have a good amount of disk heads and plates spinining and that provides me, at least on my mind, the security to get all performance for my DB.
Miguel.
One question, do you know if the SAN pool's you're using for different disks/LUNS are different physical sets? I've seen some SANs that pool a lot of drives, then cut up the pool, so it appears I have a m: drive and a l: drive, but it's the same physicals underneath.
Hi Steve,
In my case I know what is the size of the hard drives on the san, so I allocate space bigger than the capacity of a single drive. With this I´m sure that I am using at least two hard drives. Since the space is cheap I can have that luxury.
Miguel.
October 31, 2017 at 6:42 pm
mig28mx - Tuesday, October 31, 2017 1:34 PMHi Steve,
In my case I know what is the size of the hard drives on the san, so I allocate space bigger than the capacity of a single drive. With this I´m sure that I am using at least two hard drives. Since the space is cheap I can have that luxury.
Miguel.
Nice, I like rules of thumb like this.
November 2, 2017 at 1:57 pm
I have been running SQL Servers on NetApp via direct attached physical hosts via ISCSI as well as pure virtual machines. I usually separate data/log/tempdb to manage storage and have rarely come across performance issues. I have not asked our outsourced storage admin about RAID configs but the only performance differences I can see are between the various disk types in our storage pool (SSD, SAS, SATA).
November 4, 2017 at 11:23 am
mig28mx - Tuesday, October 31, 2017 1:34 PMSteve Jones - SSC Editor - Friday, October 27, 2017 11:02 AMOne question, do you know if the SAN pool's you're using for different disks/LUNS are different physical sets? I've seen some SANs that pool a lot of drives, then cut up the pool, so it appears I have a m: drive and a l: drive, but it's the same physicals underneath.Hi Steve,
In my case I know what is the size of the hard drives on the san, so I allocate space bigger than the capacity of a single drive. With this I´m sure that I am using at least two hard drives. Since the space is cheap I can have that luxury.
Miguel.
As with many generalization there is a bit of a problem with this logic. The size of the physical drives within the device has no bearing on the way the files are laid out. If you have a SAN there are logical divisions within it that determine what disks are used. From what I've seen over the years you are always going to be striped across multiple drives. Whether you're striped across four drives or forty depends on how the SAN engineer has configured it.
We use NetApp and EMC where I work and the logical organization inside each is completely different. With a SAN about the best you can hope for is that your databases are not on a LUN that is sharing space on a disk pool with another LUN that is very active. The old rules of disk isolation still apply, it's just that we've gotten used to the performance we are "allowed" to have coming from the SAN.
Richard L. Dawson
Microsoft Sql Server DBA/Data Architect
I can like a person. People are arrogant, ignorant, idiotic, irritating and mostly just plain annoying.
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