Re: To extend or not to extend? That is the question.

darky — Mon, 19 Jan 2009 18:48:29 -0000

To answer you first question, I do not have ADHD meds. To answer your second and third question, we are talking about extents. The reason snapshots were mentioned is due to the fact that they are the primary reason a datastore runs out of space unexpectedly which requires the volume to be extended or snapshots to be commited in order to free up enough space for you to power on the VM. I left that more or less as implied as this article was written for people that may have already run into this issue before and would recognize the immediate connection between the two.

If your extents are on the same physical LUN then this article does not apply to you because there is no dependency. I thought this was clearly stated in the 2nd paragraph. While we are on the subject though, I should mention that while extents on the same LUN do not have dependency issues, that LUN can only be expanded 3 times as you are only allow 4 primary partitions per LUN. In addition to this, if the partition table for that LUN was ever wiped out (many ways this can happen), it is an extremely messy operation to recalculate the original partition boundaries. Other than those two points, using extents on the same LUN is fine.

There was really only one main reason not to use extents in this article and that is purely the dependecy factor it has with another LUN. From that one caveat alone spawns a whole series of issues. There are plenty of reasons and benefits to using extents however this one downside far outweighs any positive result that long term extent usage will get you.

I hope this clears things up for you.

Re: To extend or not to extend? That is the question.

darky — Mon, 19 Jan 2009 18:38:20 -0000

I am pleased to see you mention lock contention as it isn't something I brought up in the post. The reason I didn't mention it was because such a design only benefits Hitachi based arrays (HDS and HP XP series) since they are slow to lock and unlock SCSI-2 based SCSI reservations.

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Re: To extend or not to extend? That is the question.

Re: To extend or not to extend? That is the question.