[illumos-Discuss] md aka svm aka lvm

[Haudy Kazemi]

Kyle McDonald wrote:
>
>
> On 8/29/2010 12:37 PM, Andre van Eyssen wrote:
>> On Sun, 29 Aug 2010, Bryan Horstmann-Allen wrote:
>>
>>> How is "disk concatentation" different than:
>>>
>>>  # zpool create test $PWD/1 $PWD/2
>>
>> Because ZFS will load balance approximating a stripe in that 
>> situation, as opposed to a straight concatenation available with 
>> DiskSuite.
>>
> True that is a difference. But is that bad? When is straight 
> concatenation more desirable?
>
>   -Kyle 


RAID0 = striping
JBOD = straight concatenation

Neither has any redundancy, however the potential impact of a failure is 
different.    JBOD failure has the potential of being less severe than 
RAID0 failure.  With JBOD, most likely you will only lose the content of 
single drive that failed (the remaining content has some chance of being 
recoverable).  With RAID0, you lose everything larger than the stripe 
width, which means any medium or large files, because they have been 
striped across multiple drives.  The smaller files fit within a stripe, 
so they should still be recoverable assuming the drive they ended up on 
is still working.  (Actually, with RAID0, a failed drive just about 
guarantees your medium and large files have holes in them, while with 
JBOD those files might have holes in them because of fragmentation.) 

Some caveats that apply are the effects of file fragmentation and the 
potential loss of filesystem tables/metadata.  In either case, if you 
lose the filesystem tables/metadata, you will need to file carve out 
anything that remains, and file carving doesn't work very well on 
fragmented files.