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When I set up my mirrored software RAID (two 200GB SSD drives in a Mac Pro), I neglected to check "Automatically rebuild RAID mirror sets". I would like to change this setting. My mirror is my boot volume.
Is there a way to change this after the fact? Maybe from the command line?
Mac Pro, Mac OS X (10.6.7)
No, it must be onfigured when the array is set up. FWIW, RAIDs should not be used for a startup volume. They are intended to provided storage or backup solutions.
Cannot tell you more because you have not provided any information as to what specific problem you have with the array.
I'm not having any problems with the array. I just neglected to check that box when setting it up, and need to enable that functionality. I hate to have to wipe and rebuild the whole array to change one setting.
Why would you not use a RAID1 mirror as a boot volume? I have been doing so for many years with many machines. It has saved me (and my data) through several drive failures. OS X software RAID has always been very robust.
If you said you were using mirror RAID for backup, that would also get you the same lecture ;-)
Actually though, both from RAID and SSD point of view, redundant backups are a must. That means clone your RAID volume and keep that someplace handy. Can even be a sparse disk image (.DMG) if you want, or just another bootable backup volume (so you can run repairs).
While you might think it helps to have a mirror, I doubt it is going to help protect that much from a failure. There is no TRIM obviously. And given Apple's RAID implementation, it isn't multi-threaded, doesn't take advantage of other features, I would buy SoftRAIDfor its support, features. Robust is not a term I would use for Apple's.
And restoring a RAID from clone should be done regularly when using SSD, and a must in any case.
Personally, with the amount of drive bays and SATA bandwidth, I think there are better uses for the 4-5 drive bays.
And, to add to the hatter's response:
RAID Basics
For basic definitions and discussion of what a RAID is and the different types of RAIDs see RAIDs. Additional discussions plus advantages and disadvantages of RAIDs and different RAID arrays see:
RAID Array and Server: Hardware and Service Comparison.
Hardware or Software RAID?
RAID Hardware Vs RAID Software - What is your best option?
RAID is a method of combining multiple disk drives into a single entity in order to improve the overall performance and reliability of your system. The different options for combining the disks are referred to as RAID levels. There are several different levels of RAID available depending on the needs of your system. One of the options available to you is whether you should use a Hardware RAID solution or a Software RAID solution.
RAID Hardware is always a disk controller to which you can cable up the disk drives. RAID Software is a set of kernel modules coupled together with management utilities that implement RAID in Software and require no additional hardware.
Pros and cons Software RAID is more flexible than Hardware RAID. Software RAID is also considerably less expensive. On the other hand, a Software RAID system requires more CPU cycles and power to run well than a comparable Hardware RAID System. Also, because Software RAID operates on a partition by partition basis where a number of individual disk partitions are grouped together as opposed to Hardware RAID systems which generally group together entire disk drives, Software RAID tends be slightly more complicated to run. This is because it has more available configurations and options. An added benefit to the slightly more expensive Hardware RAID solution is that many Hardware RAID systems incorporate features that are specialized for optimizing the performance of your system.
For more detailed information on the differences between Software RAID and Hardware RAID you may want to read: Hardware RAID vs. Software RAID: Which Implementation is Best for my Application?
No offense, but you are throwing a lot of assumptions around that don't really answer my question.
- Yes, I know RAID isn't for backups. I backup daily. What RAID1 does do is let you keep on working through a drive failure, which is critical in my scenario. It's great to keep things going until the evening when you can liesurely shut down and replace the disk.
- TRIM support isn't necessary on my SSD, as its controller performs the same function internally.
- I haven't used SoftRAID since having serious problems with it a few years back.
- I have found Apple's RAID to be very robust, and an exellent performer over many years of use on many systems.
While you might think it helps to have a mirror, I doubt it is going to help protect that much from a failure.
I have had several instances accross many OS X machines set up this way over the past few years. It goes like this: One of the drives begins to fail and throws SMART errors or just degrades. Without the array, I may have just had a crash. Instead I continue to work until the end of the day and replace the drive with my standby. OS X rebuilds the RAID overnight and all is well.
Anyway, none of this has anything to do with my question; although it's an interesting side discussion :-)
Wow, Kappy; that paste from Adaptec's website (I assume) is totally off topic.
Back to the original topic:
Does anyone know if there is a way to change the "Automatically rebuild RAID mirror sets" setting on an OS X RAID1 mirror after it has already been running?
Kappy says "No, it must be onfigured when the array is set up." This is incorrect.
To answer my own question:
I was doing "man diskutil" today, and ran across this:
appleRAID raidVerb [...]
update key value raidVolume
Update the key value parameters of an existing RAID set. Valid keys are:
o AutoRebuild - If true, the system attempts to rebuild degraded mirrored
volumes automatically. When looking for devices for rebuild, AppleRAID
first looks for hot spares and then degraded members. Use a value of "1"
for true and "0" for false.
o SetTimeout - Controls how long the system waits (in seconds) for a missing
device before degrading a mirrored raid set. Also controls the amount of
time you have to disconnect all devices from an unmounted mirror without
degrading it.
So I did:
diskutil appleRAID list
which showed that my RAID 1 is "disk2"
and Rebuild: manual
Then I did:
diskutil appleRAID update AutoRebuild 1 disk2
diskutil appleRAID list
now Rebuild: automatic
Problem solved.
Some advice, if I may: When posting on a discussion; quality is more valuable than quantity. If you don't know the answer, don't answer at all. There's a lot of off topic info in your posts -- which may be useful to folks new to RAID -- but none of it was pertinent to the topic.
Well, it's not from Adaptec's website. It's not off topic. And, I answered your question in my first post. Here's a reminder:
"No, it must be onfigured when the array is set up." How much more pertinent do you desire?
Here's some advice from me. If you aren't going to carefully read the responses or aren't happy with the word "NO," then you shouldn't be asking questions here. The material I've provided to you isn't off-topic. It was and is quite pertinent. But you just don't like to read what it says.
I'd say you were now being quite rude. So much for your quality. Intelligent reading is more important than simply rejecting a post because it's too long for your attention span. And, based on your question I would surmise you are new to RAIDs.
"NO" is not the correct answer though. The answer is a one line command (as I described):
diskutil appleRAID update AutoRebuild 1 disk2
Where "disk2" is your RAID volume. This changes the "Automatically rebuild RAID mirror sets" setting to true (checked box).
I apologize if I came off as rude. That was not my intent.
Many thanks Mark! Your diligence save me three hours of an array rebuild! (Which I was about to do when I forgot to check "Automatically rebuild RAID mirror sets" in Apple's Disk Utility.)
Thank you for not accepting 'No' as the only answer.
Thanks also Mark!
Will add that the keyword is case sensitive:
dkelly@clumsy {356} sudo diskutil appleraid update autorebuild 1 disk4
Error updating RAID: Could not modify RAID (-9960)
dkelly@clumsy {357} sudo diskutil appleRAID update AutoRebuild 1 disk4
The RAID has been successfully updated
Error -9960 seems to be universal error because if you try to set AutoRebuild to its current value you get -9960 error:
dkelly@clumsy {358} sudo diskutil appleRAID update AutoRebuild 1 disk4
Error updating RAID: Could not modify RAID (-9960)
Others surfing this subject might also be interested to know just as Disk Utility.app GUI can not set AutoRebuild after the fact it can not promote an existing filesystem into a RAID-1 mirror, but its relatively simple from the command line. This is the kind of thing you might do on a Mac Mini Server to pair the internal drives in RAID-1 without having to wipe/format/install. The targets will be different than I use in my example:
This is a live disk with real data:
sudo diskutil appleraid enable mirror disk3s2
Use this to discover the above created disk4:
sudo diskutil appleraid list
And then this adds the 2nd member to the mirror. Any prior contents of disk2s2 will be replaced with the contents of disk3s2:
sudo diskutil appleraid add member disk2s2 disk4
Using this technique one could clone a live filesystem to another disk, then break the RAID and have two identical drives. The man says the 2nd drive must be equal or larger in size so perhaps this would be a practical means of migrating to a larger drive?
Changing "Automatically rebuild RAID mirror sets" setting
