External JBOD enclosure + quick question

Discussion in 'Mac Accessories' started by blurobot, Feb 11, 2014.

  1. blurobot macrumors member

    Joined:
    May 28, 2009
    #1
    Just got my nMP! That thing is awesome and drive my 3 led cinema display perfectly. Just a few questions:

    - I tested jbod and it worked fine in my external enclosure with 8 disks but I wanted to test removing a disk. I did and everything broke (of course). Now what if I need to access the files on the other disks? there is no utility I know of that can recover data from all the other disks. I tried googling and came up empty. any ideas? Raid mirror worked fine and my files are intact but there's too big a penalty cost there.

    - is there any way to remove the annoying eject icon? I get why it's there but apple surely know that most external storage from a nMP is NOT ejectable and shouldn't be.

    - any way to do software raid 5 on mac with a trusted solution without hardware cards?

    anyone?
     
  2. AidenShaw macrumors P6

    AidenShaw

    Joined:
    Feb 8, 2003
    Location:
    The Peninsula
    #2
    Usually with JBOD just the removed disk will disappear, and then reappear when re-inserted. (A reboot might be needed if the enclosure/controller/drivers don't support hot-plug.)

    Even with RAID-0 the usual behavior is that the volume disappears when one drive is removed, then reappears when it is re-inserted.

    What exactly was your setup?
     
  3. deconstruct60 macrumors 604

    Joined:
    Mar 10, 2009
    #3
    You are doing spanning ( concatenation) of 8 disks or real JBOD where 8 (or more ) different storage volumes show up on the desktop/Finder. If used 8 disks and have one volume on desktop/Finder then it wasn't JBOD.

    The files are likely about as screwed up if had RAID 0 stripe set of 8.


    If this is real JBOD ( there were 8+ volumes ) then should be able to force a restart of the disk enclosure to bring them back.


    Given the drive can be detached, the eject icon should stay. "Eject" is just the legacy word that is most associated with the "unmount" action.
     
  4. AidenShaw macrumors P6

    AidenShaw

    Joined:
    Feb 8, 2003
    Location:
    The Peninsula
    #4
    If the software/hardware works like most, removing a RAID-0 member should suspend the volume, not destroy it.

    Replacing the member should resume the volume.
     
  5. blurobot thread starter macrumors member

    Joined:
    May 28, 2009
    #5
    I know there's a bunch of jbod terminalogy so let me clear things up:

    In disk utility i used concatenated disk set so I can have 1 logical volume over 8 disk. Now I'm trying to simulate 1 disk going bad so I remove one. The entire logical drive now unmount. But if I put the disk on another mac will i see the files there? it says it's a missing slice when I put it back on. If i reboot everything is back online but my real question is how can i retreive the info on all remaining 7 disks if 1 fail?

    I'll have backup but I want it to be as painless as possible.


    secondly the eject icon question in finder: I want to remove the arrow so it looks like a real internal disk so i dont misclick it. Can I do that? Any crazy terminal command? surely all these new nMP owner don't want their disks to be ejectable.
     
  6. AidenShaw macrumors P6

    AidenShaw

    Joined:
    Feb 8, 2003
    Location:
    The Peninsula
    #6
    With a concatenated disk (or RAID-0) if any disk goes bad all data will be lost. You can't remove a bad disk, insert a new one, and rebuild. That only works with RAID-1/10/5/6/50/60 and other varieties with redundancy.


    The files (and filesystem metadata) are scattered across all of the disks. Any single disk won't have all the pieces needed to see anything. Anything less than the full set won't work.


    Backups. Or use RAID-6.
     
  7. FireWire2 macrumors 6502

    FireWire2

    Joined:
    Oct 12, 2008
    #7
    JBoD - you should be able to remove a drive, unless what you have a a SPAN(BIG). Lots of manufacture mislead users by calling SPAN/BIG is JBOD

    You can use a stand-alone raid5/JBoD enclosure like this
    http://www.newegg.com/Product/Product.aspx?Item=N82E16816119031

    http://www.amazon.com/Dual-Thunderb...e=UTF8&qid=1392158289&sr=8-5&keywords=tRAID-T

    There is no drivers/software need


    Update: ----------

    If the volume is not written, then is very good chance you can have your data back fairly easy.

    Use this software http://www.cgsecurity.org/wiki/TestDisk_Download

    Your Partition Table is corrupted
     
  8. blurobot thread starter macrumors member

    Joined:
    May 28, 2009
    #8
    Aiden I understand raid0 but isn't raid0 the stripped option in disk utility and concatenated the jbod option?

    I'll try that software thanks!
     
  9. AidenShaw, Feb 11, 2014
    Last edited: Feb 11, 2014

    AidenShaw macrumors P6

    AidenShaw

    Joined:
    Feb 8, 2003
    Location:
    The Peninsula
    #9
    JBOD means "Just a Bunch Of Disks" - you'd have 8 volumes (or logical disks) with no interdependencies. You'd see 8 disks/volumes/filesystems that were completely separate. Removing one disk would mean that you had 7 complete volumes, and one missing. You'd have all of the files on the 7, and none of the files on the 8th.

    RAID-0 is "striped". The logical volume is spread across the physical drives with a certain "chunk size", typically in the 64 KiB to 256 Kib range. The first chunk is on disk 0, the following chunk is on disk 1, repeat.... If you lose a disk, every "nth" chunk disappears, and the data is unusable.

    If you initialize a concatenated volume with "n" identical drives, you'd have essentially RAID-0 where the "chunk size" is the drive size. Since filesystems often place meta-data in different locations (e.g. putting less often referenced data at the slower "high" blocks at the end of the drive), no single drive (or less than the full set) will have all of the data and metadata needed to access the files.

    In practice, concatenated filesystems usually can be expanded on the fly, with chunks of different sizes. That means that sometimes some concatenated volumes can access older files if the newer chunks are not accessible. Don't depend on this, however. While in theory some files might be accessible, the volume managers will typically throw an error and refuse to mount a volume with a "missing slice".


    If you like your data, in your case go with RAID-50 or RAID-6. If you want backups to be your recovery strategy, go with RAID-0. RAID-0 is just as unreliable as concatenated, but is faster.
     

Share This Page