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Old 07-11-2006, 07:42 PM   #1
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Question Should I use JBOD or LVM? (spanning disks)

Hi, I have a Tyan s2865 motherboard which supports hardware JBOD (spanning).

I was trying to decide whether I want to use LVM or JBOD for my 2x 500GB and 1x400GB drives, and came up with a few concerns about both.

My main concern with using the hardware JBOD was the master file table. I am concerned that if I put an ext3 partition on spanned disks the MFT may only exist on one, or expand to others without the files listed in it virtually making the system dependant on the drive with the MFT entry and in the case where the drive may fail I might lose all my files. The secondary concern I had with JBOD is I dont know that I would be able to get the drives to powerdown after inactivity.

LVM on the other hand may or may not have performance issues compared to the JBOD volume, and I fear I would not be able to access the data on these drives within windows.

If anyone with greater knowledge of how the MFT, and hdparm suspend works on a JBOD system, or can address any of my other concerns I would be glad to hear a reply.
Old 07-15-2006, 10:42 AM   #2
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I don't know MFT but remember there is a limit to the number of partitions you can put on a drive. Presumably a spanned JBOD would appear to the OS as a single drive so you'd have a limited number of partitions for filesystems. LVM by comparison would allow you to make as many logical volumes (think of them as virtual partitions) as you'd like.

On the flip side as you mentionn LVM being software based may give slightly less performance than a hardware spanned device. Truthfully though I've used LVM for years (first on HP-UX then on Linux) and really never saw any major performance impact.

The problem with losing a single disk would be the same with either option.

It would be nice if your MFT allowed for RAID so you can have mirroring or RAID 5 because this would specifically prevent loss of a single drive from affecting you.

An option you didn't mention is software RAID. Have a look at the man page for mdadm (man mdadm). This is good on Linux as it allows you define partitions of different disks as RAID members rather than requiring the entire disks. You could therefore make your boot/root mirrored and risk the rest of your filesystems without RAID protection. In the event of a disk failure you'd lose data (assuming you weren't backing it up on a regular basis as you should) but would still be able to boot up from the remaining drive.
Old 07-20-2006, 08:07 PM   #3
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Well, even though I'm slightly paranoid about data loss, I am a college student on a slight budget, and my data files are not mission critical, so mirroring (or buying a raid 5 controller and using partity) is out of the question. (though it would have been nice if the MFT alone could be duplicated efficiently)

I went ahead and used LVM at the cost of a performance hit and lack of windows support, I did this so that I can utilize power management on the drives safely. I am also using a different, single drive, for the OS and other slightly more important files.

Thanks for the input.

Last edited by sillygates; 07-20-2006 at 08:10 PM.


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