[OSX-Users] Re: More backup questions, was: Re: backing up while on road away from time capsule

[Jules Field]

On 17/09/2011 15:11, Hugh Glaser wrote:
> Thanks.
> I was wondering if I gave it 3 disks to start with it would offer me the RAID 5 option - one can hope :-)
Yes, you can do RAID 5 on 3 disks, no problem. You'll get 2 disks of 
usable space. But they will have to be wiped to start with when the RAID 
volume is built.
> But I think I did see somewhere where they say the only options are the ones given (0&  1).
Ah, if it can only do striping (0) and mirroring (1), then you're 
obviously out of luck. Not much of a RAID system if it can't even do 
RAID 5. RAID 6 is the best, but not many small systems support it, and 
it's only really necessary when you've got multi-Tbyte RAID volumes.
> And presumably if I gave it 3 and said Stripe, it would Stripe across all three, not change to RAID 5.
Yes, should do a 3 disk stripe (0).
> Can you hazard a guess on Q1, based on your vast experience?
> Or don't you guess? :-)
It depends entirely on the system. It is perfectly possible, yes. But 
whether your particular RAID controller supports it is another matter. A 
lot of software RAID systems do.
>
> What really pisses me off is forums that don't date the messages - I keep finding a post on OSX RAID, only t6o realise it is talking abut panther, or earlier.
:-( Often Google will tell you the date it read the page, which will 
give an indication of the most recent date it has changed.

Jules.

P.S. On Mac OS X Server, I have only ever needed a simple 2-disk mirror, 
so I've never investigated its abilities beyond that.


>
> On 17 Sep 2011, at 14:23, Jules Field wrote:
>
>>
>> On 16/09/2011 19:14, Hugh Glaser wrote:
>>> On 15 Sep 2011, at 11:45, Jules wrote:
>>>
>>>> Lion will continue to do Time Machine backups to spare space on your laptop's own hard disk while it's away from its Time Capsule. Obviously this is no protection against disk failure, but it does provide protection against accidental file deletion or corruption.
>>> Wow. I didn't see that. That is really cool - just what I want it to do.
>>>
>>> New questions (there seems to be precious little about this on the net):
>>> I think I'm going to Mirror RAID my TV programmes, etc. disk, as protection against device failure.
>>> 1) Can I create a Mirror RAID Set using Concatenated Disk Sets as the components?
>>> 2) If I add more than two Disks (or Concatenated Disk Sets) to the RAID Set, will it do the clever stuff to give me RAID 5, or whatever? I am guessing not - it will just do multiple mirrors?
>> It won't do (2), you would only ever end up with more faces to the mirror. Converting a RAID 1 mirror into a RAID 5 requires a total reorganisation of the data, they are *very* different beasts. AFAIK nothing will automatically convert a RAID1 to RAID5 just because you add more disks, I've certainly never seen anyone's product attempt that trick. If it were to do it, you would lose all redundancy (and therefore safety) while it attempted to do it, and it will take a very long time to achieve.
>>
>>
>> Jules
>>
>> -- 
>> sysjkf at ecs.soton.ac.uk
>>

Jules

-- 
sysjkf at ecs.soton.ac.uk