Camniomad
Level 1 (0 points)

Q: RAID Boot with SSD's

Is it possible in Mac 10.6.7 to boot from two SSD drives in RAID from a PCI-e SATA III card?

Mac Pro, Mac OS X (10.6.7), 2x2.8 Ghz 6 GB Ram

Posted on May 22, 2011 10:06 PM

by Kappy,Solvedanswer
Kappy Kappy
Level 10 (271,284 points)
Desktops
A:

There is only one thing a RAID  provides - more space.  Beyond that a RAID can’t help you with:

 

  1. Accidental deletion or user error
  2. Viruses or malware
  3. Theft or catastrophic damage
  4. Data corruption due to other failed hardware or power loss
  5. Striped RAIDs have a higher failure risk than a single drive

The purpose of a RAID is to provide high speed mass storage for specialized needs like video editing, working with extremely large files, and storing huge amounts of data.

 

If your array fails it means complete loss of data and hours of time to rebuild.  RAIDs degrade over time necessitating many hours of restoration.  And, if you don't know much about RAIDs then you really don't need one.

 

You can use a RAID for backup.  But unless your backup needs involve TBs of data requiring rapid and frequent access, why bother?  TM works in the background.  It's not like you have to sit there waiting for your backup to be completed.  Furthermore, you're buying two drives possibly to solve a problem where a single drive will do.  And, one drive is less expensive than two.

 

Ignoring overhead two drives in a RAID 0 (striped) array should perform about twice as fast. However, as the array fills up with files that performance will degrade.

 

RAID was a technology that in it's time was meant to solve a problem.  Large capacity, fast drives were extremely expensive.  Small drives were cheaper but slower.  However, combining these cheaper drives into arrays gave faster performance and the larger capacity needed for data storage needs.  Thus, the reason why it's called Redundant Array of Inexpensive Drives.  But today you can buy a 3 TB drive with performance that's better than the 1 TB drives of two or three years ago.

 

But why trust your boot drive to a RAID?  I certainly wouldn't.

Posted on May 22, 2011 10:41 PM

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Camniomad

Q: RAID Boot with SSD's

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  • Helpful answers

  • by Kappy,

    Kappy Kappy May 22, 2011 10:11 PM in response to Camniomad
    Level 10 (271,284 points)
    Desktops
    May 22, 2011 10:11 PM in response to Camniomad

    Best to ask the card mfgr.  If it won't support booting from a single drive then it surely won't support booting from a RAID.

     

    Personally, I would recommend against using a RAID array as a boot volume.

  • by Camniomad,

    Camniomad Camniomad May 22, 2011 10:17 PM in response to Kappy
    Level 1 (0 points)
    May 22, 2011 10:17 PM in response to Kappy

    I am running out of space on a single 64 GB SSD boot volume. A cheap fix would be to slap a second 64 Gb Crucial SSD in a RAID array to boot from.

     

    I was hoping to move my user files off my boot volume, but from what I read, Apple no longer allows that in the latest versions of OSX.

     

    Why would you recommend against it?

     

    Can I back up the boot volume in a RAID array using Time Machine? Would that provide sufficient backup.

     

    How would performance be for 2xSSDs in a RAID array versus just 1.

  • by Kappy,Solvedanswer

    Kappy Kappy May 22, 2011 10:41 PM in response to Camniomad
    Level 10 (271,284 points)
    Desktops
    May 22, 2011 10:41 PM in response to Camniomad

    There is only one thing a RAID  provides - more space.  Beyond that a RAID can’t help you with:

     

    1. Accidental deletion or user error
    2. Viruses or malware
    3. Theft or catastrophic damage
    4. Data corruption due to other failed hardware or power loss
    5. Striped RAIDs have a higher failure risk than a single drive

    The purpose of a RAID is to provide high speed mass storage for specialized needs like video editing, working with extremely large files, and storing huge amounts of data.

     

    If your array fails it means complete loss of data and hours of time to rebuild.  RAIDs degrade over time necessitating many hours of restoration.  And, if you don't know much about RAIDs then you really don't need one.

     

    You can use a RAID for backup.  But unless your backup needs involve TBs of data requiring rapid and frequent access, why bother?  TM works in the background.  It's not like you have to sit there waiting for your backup to be completed.  Furthermore, you're buying two drives possibly to solve a problem where a single drive will do.  And, one drive is less expensive than two.

     

    Ignoring overhead two drives in a RAID 0 (striped) array should perform about twice as fast. However, as the array fills up with files that performance will degrade.

     

    RAID was a technology that in it's time was meant to solve a problem.  Large capacity, fast drives were extremely expensive.  Small drives were cheaper but slower.  However, combining these cheaper drives into arrays gave faster performance and the larger capacity needed for data storage needs.  Thus, the reason why it's called Redundant Array of Inexpensive Drives.  But today you can buy a 3 TB drive with performance that's better than the 1 TB drives of two or three years ago.

     

    But why trust your boot drive to a RAID?  I certainly wouldn't.

  • by Camniomad,

    Camniomad Camniomad May 22, 2011 10:45 PM in response to Kappy
    Level 1 (0 points)
    May 22, 2011 10:45 PM in response to Kappy

    Thanks a million for your reply. Very helpful. I am convinced. No RAID for an apprentice like me.

     

    But I am still have the problem that my 64 Gb SSD is filling up and killing my performance.  What do you think about moving the Users to a separate drive, freeing the SSD just for the OS.

  • by Kappy,

    Kappy Kappy May 22, 2011 11:12 PM in response to Camniomad
    Level 10 (271,284 points)
    Desktops
    May 22, 2011 11:12 PM in response to Camniomad

    That you can do.  Use a good backup utility to backup your account folder to a separate drive.  Open Accounts preferences, click on the lock icon and authenticate.  CTRL- or RIGHT-click on your account in the list and select Advanced Options from the contextual menu.  You will see a field labeled "Home directory:" with a button on the right labeled "Choose."  Click the button and navigate to where the new Home folder is located.  Select the account folder and click on the Open button.

     

    This redirects the OS to use the Home folder located on the other drive.  On the SSD delete the contents of all the folders in the old Home folder except for the /Home/Library/ folder.  In the old /Home/Library/ folder you can safely delete all the preference files except those that start with "com.apple." and the ByHost folder.  You can also delete all the folders in the Applications Support folder that were created by your third-party applications.  You can delete the contents of the Mail, Safari, and Calendar folders and the /Applications Support/AddressBook/ folder.  You can remove the contents of the Applications folder except those you prefer to retain just in case.

     

    This will clear out quite a bit from the SSD, but leave just enough of a Home folder to use in case there's a problem with the Home folder on the other drive.  OS X must find a usable Home folder in order to start up which is why you don't want to remove the entire Home folder from the SSD.

     

    Of course you could also spend the money on a larger SSD which would make more sense.

  • by The hatter,

    The hatter The hatter May 23, 2011 4:31 AM in response to Camniomad
    Level 9 (60,935 points)
    May 23, 2011 4:31 AM in response to Camniomad

    You can do software array with two SSDs and I recommend SoftRAID 4.

    Take a look at its features, and SSD support. Great team also.

     

    SoftRAID.com

     

    Even if OS X only used 40GB I like to see free space on standard drives, even more so on an SSD for BGC and TRIM (there are some experimental driver hacks going on).

     

    And I would still do the move of your data but leave the core 1GB of your home account library folder only which can benefit a lot from beng on the SSD instead of on slower 7,2k drive.

     

    Documents, etc can also be on another drive.