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Had one of the previous generation never did raid in it but the disks in it did all show up in Disk Utility at once so would be software raidable in osx. Never did notice that the one I had would only work with three disk or less than in it until the warranty expired and I had added a fourth disk by then, the San Digital I bought to replace it all worked fine in it.
 
I want to get one of these
http://www.amazon.com/gp/product/B003X26VV4?ref_=cm_cd_al_qh_dp_t

but it does not have built in raid support
however, if I use disk utility to partition the disks,
I would be able to use the RAID feature to combine 2 hard drives into a Raid 1 array over USB 3.0?
Starting with El Capitan, Apple removed RAID support from Disk Utility. It is no longer possible using the GUI to create a RAID volume or even to verify the integrity of that volume in the event of a crash or uncontrolled shutdown.

You have three choices:

(1) Use terminal commands to create a RAID volume
(2) Purchase and use SoftRAID Lite: https://softraid.com/pages/features/softraid_lite.html
(3) Only buy hardware RAID systems
 
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Starting with El Capitan, Apple removed RAID support from Disk Utility. It is no longer possible using the GUI to create a RAID volume or even to verify the integrity of that volume in the event of a crash or uncontrolled shutdown.

You have three choices:

(1) Use terminal commands to create a RAID volume
(2) Purchase and use SoftRAID Lite: https://softraid.com/pages/features/softraid_lite.html
(3) Only buy hardware RAID systems
(4) Use the Disk Utility of an older version of OS X, e.g. on an installable thumb drive.
 
Older versions won't run on El Capitan.

Thus the flash drive.

I've got a couple Mac Pros at the office running internal software RAID 0 drives for video editing and a HW RAID 5 for storage. It was created under Mavericks and after updating to El Capitan it still works but isn't editable/viewable in Disk Utility. But if I boot to my Mavericks USB installer I can use Disk Utility from there (outside the OS) and it still works just fine.
 
I'm still running yosemite
seems like the option is there

if I set the raid up in disk utility on Yosemite
and then upgrade to el capitain
everything is going to continue to run properly?
thanx for the replies

if I can't raid, that's fine
is there some free Folder to folder sync tool you recommend?
 
You can still RAID the disks, but you'll need to do it via the Terminal and use diskutil. Using a RAID 1 setup, is a nice way to protect your data since it will be mirrored.
 
...
if I set the raid up in disk utility on Yosemite
and then upgrade to el capitain
everything is going to continue to run properly?...


It will function OK but in the event of a crash or uncontrolled shutdown you cannot verify the disk file system using Disk Utility. So the impact of removing this functionality is broader than just those who want to create a new software RAID volume. It affects those already using a software RAID volume, who upgrade to El Capitan, then need to verify the disk.


Starting with El Capitan, this cannot be done with the GUI but only with terminal commands, with a 3rd party utility or by booting the disk to an older version of OS X. However I don't think you can boot to a back level OS X on the new 2015 iMacs so that's not an option for those users.
 
From what I understand (according to Mac Performance Guide) that there is a nasty bug in HFS+ and/or the RAID implementation which apparently can cause issues. I've got a Drobo 5D device - their previous generation of NAS devices were shockingly slow but the Drobo 5D hooked up to the thunderbolt port has been working great for over a year since I purchased it.
 
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