Recommendation for external hard disk and connection type for Macpro

bozer used Ask the Experts™
Hello experts,

I need some guidance and to hear your similar experiences regarding External Disks used with Macpro. I am a new Mac user, I could not resist to get a 16 GB RAM on a laptop which is offered by Macpro by default.

I am traveling frequently and I need to use several VM images at the same time so I thought this machine would be a life saver. However, I keep having issues when I try to turn on more than 3 VM images from an external disk. I tried 3 types of external disks: one with USB 2 (separate electricity), USB 3 (separate electricity), USB 3 (electricity through USB interface)

All three trials ended with freezes and I strongly suspect that the problem is from the disk I/O speed.

To address this problem once and for all, I want to investigate my options:
1. I cannot copy my VMs on Macpro's disk for space limitations. I need to carry them on an external device.
2. I need to get/buy an external disk that will give me a reasonable I/O so that I can acceptably run 3-4 VMs at the same time
3. I need to choose an interface that provides me the fastest communication between the external device and macpro. USB 3? Firewire?
4. Will the performance be better if I invest on a big size SD card instead and have my VMs in it?
5. What are your methods and experiences?

Please share comments and ideas.

Thank you in advance.
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Zephyr ICTCloud Architect

If you want performance from your VM's you need to have good IOPS, if you want good IOPS your best bet is a SSD drive ... Now to take advantage of this speed a minimum of USB3 will be required, but if possible I'd go for Thunderbolt.

Something like the LaCie Rugged USB 3.0 Thunderbolt  or the Elgato Thunderbolt SSD would do nicely.

If that still gives you issues, then I'd look for the problem elsewhere...
You haven't mentioned what the VMs are doing,  but the fact you have 3 of them and one HDD, probably   means an IOPS squeeze;  faster spindles or more spindles  (e.g.  RAID10 enclosure with 4 or 5 disk drives and at least 256 megabytes of NVRAM-backed write cache) could go a long way.

Another thing to consider is chaining multiple external disks and running each VM on a different one,  when all 3 are running simultaneously.

"4. Will the performance be better if I invest on a big size SD card instead and have my VMs in it?
No.  Forget SD cards; too little write durability, they will be toast under the write load of any relatively normal VM,  let alone 3 VMs doing normal disk activities.     What you really need here is a SSD;  preferably with a DRAM cache.  An  Intel 700 series SSD such as the SSDSA2BZ300G301, SSDSA2BZ300G3   fits the bill in terms of performance,  but  at  at  $1200 it's a big ticket item.

I would look at the Crucial M500s, which are about $200 for 240gb, or $300 for 480gb,  then .   a  SATA to USB3 or SATA to Thunderbolt drive enclosure;  despite there is less cache, and the units certainly less reliable  and lower durability than the Intels.

You should be able to run at least 4 or 5 VMs on a decent SSD, with adequate RAM assigned to the virtual machines [We assume no truly excessive paging, memory or IO thrashing] ----  assuming   we are not doing something like massive sustained writes, or requiring massive amount of capacity (over 100gb per VM).

Areca also makes a RAID enclosure, the ARC-8050, that can supposedly handle RAID10 with 4 disk drives via Thunderbolt interface, Promise, DataTale,   and Sonnet   also have options.

RAID10 with spinning disks  may make more sense if your VMS require a large amount of disk space,  or sustained write behaviors.

RAID on a desktop system with multiple disk drives is a boutique solution, though,  commonly used for high-end video editing, and the price  of the available solutions reflects that.

A few SSDs in a dedicated external Thunderbolt or USB 3.0  enclosure  ----- is certainly a more portable idea!

Individual 2.5" SSDs are lightweight,  and  RAID enclosures that can accomadate at least 4 disks -- are huge and heavy  power consuming beasts, esp. when fully loaded.


Hello again,

I appreciate your recommendations. Based on your comments, I am on the right track to assume my issue is the I/O. I recently purchased a WD 2 TB USB 3 supported disk but it looks like I'll pay the price of not researching this through... I checked quickly and will do more but I found this which may fit in my budget (and targeted size):

Please advice if this product is similar to what you are suggesting? I guess there are so many options with several brands around. I don't want to get another brand with 500GB when I can get this with the same price (1 TB) unless it is significantly worth it.

As for SSDs, I think they are way out of my budget for now. I think I need at least 500GB but that size is a small fortune for SSD drives. Does it really worth it?


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Cloud Architect
All I can say is that I have both a USB3 with a SATA 6Gb/s 7200rpm HDD and a SATA3 SSD, both aren't comparable at all as well as a Thunderbolt SSD ... I stated that Thunderbolt is a requirement, but actually, if you could spring for a SSD with USB3 that would suffice, USB3 is 6GB/s so that is at the top anyway, Thunderbolt wouldn't really be a benefit. This site explains the difference:

As for my experience: I can run 1 VM well on the 7200rpm HDD, two is stretching it ...
On the SSD I can run a complete virtual VMware lab (3 ESX servers) without loosing much performance...
@Bozer - What you have to understand that a single HDD of the type you suggested can only do 150MB/sec (spec actually says 136MB/s) and around 100 IOPS, whereas a SSD should be able to  do 400+MB/s and 1000's of IOPS.

So if your VM problem really is down to IO performance, and from your description it would seem so, then the use of a SSD would seem to be a nobrainer.

Just because an interface (e.g. USB3/Thunderbolt) looks to be a bigger pipe, it doesnt neccessarily follow that it is faster in real life. see this article which might surprise you macworld how-fast-is-usb-3-0-really


Thank you for your inputs. I decided to buy a 120 GB SSD Lacie Thunderbolt USB 3.0 disk as soon as possible.

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