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As a company we are going for a new server that will run hypervisor and host another 3 VMs - Two business systems + VM with Sql Server only (Equivalent of AWS RDS)

Operating systems of each VM and hypervisor will use SSD as a storage. VMs and database will use HDD 7.2k in raid 1.

We have enough processing power and RAM (128GB) but what worries me a bit is that the RDS equivalent (Sql Server VM) will be using main server storage (HDD 7.2k 4TB in raid 1) as a storage.

We don't tend to stress those systems to the limits, they will rather run websites with on-line shops, so shouldn't be very I/O intensive) It's difficult to give any numbers at this point as we don't know how the traffic will look like.

From what I see already HDD may be a bottleneck here but heard when researching net and forums that the massive RAM we have may eliminate it. Is it really the case?

Regards

ps. I cannot change the server spec or attach any additional storage unfortunately.

Server specs: https://www.fasthosts.co.uk/sites/fasthosts.co.uk/files/1370_Data_Sheet_1.pdf

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This depends. Seriously. Nothing in virtualization changes the basic rules of disc layout. The Server hosting a intranet website for 5 people? Likely enough. THe server hosting a busy terabyte level database - attach a LOT more disc / SSD and map them directly to the VM.

Your SQL storage (HDD 7.2k 4TB in raid 1) is "pathetic" (as in: low in the world of larger SQL) and may or may not work - it totally depends on how small the server is.

But again, nothing stops you from attaching a lot more IOPS. I know a database server running in Hyper-V (with around 8 other low performance VM's on the same host) that has 48GB allocated RAM and about a dozen discs / SSD directly mapped to the VM from the underlying hardware. In a 2U rack case with 24 2.5" slots. It is easily possible.

From what I see already HDD may be a bottleneck here but heard when researching net and forums that the massive RAM we have may eliminate it. Is it really the case?

Well, let's start: " and RAM (128GB)" - that is NOT massive. Or it is. Depends on (a) how much of that the SQL VM gets and (b) how large the databases are. I have seen databases needing a lot more. I have seen databases living happy in 32gb memory.

That said, that will only help with QUERIES (read) that do NOT use tempdb (which may be written) and low transaction throughput (logfile writes). Whether it is enough for your sql server we can not answer. You have to measure that.´I have a SQ LServer here having 4x480gb ssd in a Raid 10 JUST for tempdb and 6 x 800gb SSD in 2 Raid 3 for data. And yes, it needs it - I often push around multi gigabyte datasets on that machine. Lives nicely in a VM (as I said, 48gb RAM allocated).

SOME things you can make to improove, though: * Add some SSD * Set up a storage pool on Hyper-V and attach the SSD as buffer. Voila, a LOT of buffer for often used data and / or writes. assuming you use Hyper-V in a modern version (2012R2) as host. The beaty? 240gb ssd, 2 should already bring a lot.

Otherwise - really, we will need a ton more research and analysis to make a decent advice. SQL Server disc layout is still something that may be trivial (small server) or requires a lot of thought and planning (large server).

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  • Thank you very much. The server specs we'll use are here: fasthosts.co.uk/sites/fasthosts.co.uk/files/… I know it'll be difficult to advice without any concrete numbers but I don't have them myself either yet. I cannot change the spec or upgrade server at all, not even at later stage. My hope was to put tempdb and user log files on SSD and database files together (unfortunately) with VMs, VHDs and static website data onto main storage (2TB 7.2k HDD) Sql Server VM most probably will have 64GB Ram and 1 Quad-core CPU assigned.
    – Mariusz
    Oct 23, 2015 at 12:58
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I've run busy databases on Pentium 3 servers with 4GB of ram with terribly slow SCSI drives. They were perfectly fast for my needs at the time. Your system may not be good enough, or may be more than you need.

You'll need to do some testing and research yourself to figure out what your requirements are. Lots of ram doesn't mean there will be low disk IO.

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After few years of working with this server ended up we didn't have any bottlenecks or problems with it and above spec was more than enough for what company needed.

I simply put tempdb and Windows OS on SSD and rest on hdd.

Cheers for advice anyway.

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    Thanks for the update. As you have experienced, it's really tough for other people to assist you with capacity planning, without knowing a lot more details than just available hardware and number of users.
    – mfinni
    Mar 5, 2020 at 20:05

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