Louwrentius

In Accidental Tech Podcast episode 18 (love the show), I learned that John Siracusa was thinking about buying a new Mac Pro for gaming.

I believe that gaming on the new Mac Pro will be a mediocre experience.

Driver support: as John mentioned himself, the video cards are 'professional GPUs' used in workstations for computing, CAD etc. These cards and especially their drivers under Windows are not geared towards gaming performance.

The performance and quality of Mac OS X drivers may be improved dramatically over the past years, but if you like to play games exclusively under Windows, you will probably be disappointed when you switch to bootcamp.

Crossfire support: you have these two ridiculously fast GPU's and for years on the PC platform, you can stack them together to achieve insane performance (SLI / Crossfire).

Mac OS X does not seem to support crossfire (or SLI). If you can't benefit from crossfire, you're paying a lot of money for a machine with one idle but very expensive videocard. That sounds like a ridiculous waste of good money.

Assuming that the hardware supports crossfire, if you would run Windows, then you may hit the driver issues associated with pro cards.

Upgrading: upgrading can be cost-efficient as most games are GPU not CPU bound, not an option for the Mac Pro. Even the new Thunderbolt interface does not have sufficient bandwidth to hook up one or more external high-performance videocards, aside from the fact that this will be insanely expensive.

If you really needs the horsepower of a Mac Pro for other purposes than for gaming, sure it's the fastest mac you can get, but otherwise, I believe there's a better deal to be had.

We don't now what the new Mac Pro will cost in a configuration suitable for gaming, but it will be 'a lot'. I believe that for one new Mac Pro, you will also be able to buy:

1. a mac Mini with reasonable specs (it's easy to replace memory and storage);
2. a high-quality 27" display @ 2560x1440
3. a ridiculously fast PC that will outperform the new Mac Pro when it comes to gaming.

I know that some Mac users don't like the idea of having a PC at home, but if you are into PC gaming, there's no other choice in my opinion if you want a good gaming experience.

I had high hopes for my 27" iMac (2011) but gaming performance anno 2013 is just mediocre at best. And I can't use it as an external display with a PC, only with a Mac.

So I sold my 27" iMac and used the money to buy a separate 27" display and Mac Mini. I also ordered a 'ridiculously fast PC' which I hope will allow me to play all modern games on max quality settings for now and the upcoming year. And if required, I can swap out the dual GPUs and replace them with something better over time, if I need to.

10 Gb ethernet is still quite expensive. You not only need to buy appropriate NICS, but you must also upgrade your network hardware as well. You may even need to replace existing fiber optic cabling if it's not rated for 10 Gbit.

So I decided to still just go for plain old 1 Gbit iSCSI based on copper for our backup SAN. After some research I went for the HP MSA P2000 G3 with dual 1 Gbit iSCSI controllers.

Each controller has 4 x 1 Gbit ports, so the box has a total of 8 Gigabit ports. This is ideal for redundancy, performance and cost. This relatively cheap SAN does support active/active mode, so both controllers can share the I/O load.

The problem with storage is that a single 1 Gbit channel is just not going to cut it when you need to perform bandwidth intensive tasks, such as moving VMs between datastores (within VMware).

Fortunately, iSCSI Multi Pathing allows you to do basically a RAID 0 over multiple network cards, combining their performance. So four 1 Gbit NICS can provide you with 4 Gbit of actual storage throughput.

The trick is not only to configure iSCSI Multi Pathing using regular tutorials, but also to enable the Round Robin setting on each data store or each RAW device mapping.

So I dit all this and still I got less than 1 Gb/s performance, but fortunately, there is only one little trick to get to the actual performance you might expect.

I found this at multiple locations but the explanation on Justin's IT Blog is best.

By default, VMware issues 1000 IOPS to a NIC before switching (Round Robin) to the next one. This really hampers performance. You need to set this value to 1.

esxcli storage nmp psp roundrobin deviceconfig set -d $DEV --iops 1 --type iops

This configuration tweak is recommended by HP, see page 28 of the linked PDF.

Once I configured all iSCSI paths to this setting, I got 350 MB/s of sequential write performance from a single VM to the datastore. That's decent enough for me.

How do you do this? It's a simple one liner that sets the iops value to 1, but I'm so lazy, I don't want to copy/past devices and run the command by hand each time.

I used a simple CLI script (VMware 5) to configure this setting for all devices. SSH to the host and then run this script:

for x in `esxcli storage nmp device list | grep ^naa`
do
    echo "Configuring Round Robin iops value for device $x"
    esxcli storage nmp psp roundrobin deviceconfig set -d $x --iops 1 --type iops
done

This is not the exact script I used, I have to verify this code, but basically it just configures this value for all storage devices. Devices that don't support this setting will raise an error message that can be ignored (if the VMware host also has some local SAS or SATA storage, this is expected).

The next step is to check if this setting is permanent and survives a host reboot.

Anyway, I verified the performance using a Linux VM and just writing a simple test file:

dd if=/dev/zero of=/storage/test.bin bs=1M count=30000

To see the Multi Pathing + Round Robin in action, run esxtop at the cli and then press N. You will notice that with four network cards, VMware will use all four channels available.

This all is to say that plain old 1 Gbit iSCSI can still be fast. But I believe that 10 Gbit ethernet does probably provide better latency. If that's really an issue for your environment, is something I can't tell.

Changing the IOPS parameter to 1 IOPS also seems to improve random I/O performance, according to the table in Justin's post.

Still, although 1 Gbit iSCSI is cheap, it may be more difficult to get the appropriate performance levels you need. If you have time, but little money, it may be the way to go. However, if time is not on your side and money isn't the biggest problem, I would definitely investigate the price difference with going for fibre channel or with 10Gbit iSCSI.