HDP - Response to Marc Farley

Below are some notes to the above videos (especially for those in quiet offices who can’t watch the video yet).


I posted the video in response to Marc Farleys recent video and comments on Hitachi Dynamic Provisioning, as well as other comments that have been made in blogs and on twitter etc….. All of these comments have been slating HDP for being chubby and the likes. Hopefully this post and the video will help set the record straight.

The 42MB page

On the topic of HDP being chubby. While I accept that the HDP extent (page) size of 42MB is by far the largest of all the major vendors, I do not think this is necessarily all bad. For a start it maps perfectly with the internal workings of the USP V and VM. Secondly I think there is more metadata overhead the smaller your extent size – internal tables need to be larger and then there’s metadata for replication, snapshots and the likes. The smaller your extent size, the more metatada required. May be that’s OK on a midrange box that won’t be expected to address large amounts of storage and have lots of copy services running in the background……. I just don’t think its as simple as saying “ho ho ho look at Hitachi’s huge allocation unit, that must be lazy coding from the engineers”.

Yes I know that a smaller extent might be more thin friendly, but how many enterprise customers are deploying this for the “thin” oversubscription benefits?

Oh and yes there are situations where two small writes to the same HDP volume will require two separate pages. However, this is not always the case and often not.

See this link for what I’ve written in the past regarding how perfectly aligned 42MB is with the internal structures of the USP V.

Zero Page Reclaim

Then there’s Zero Page Reclaim. Suggesting that it’s an apology rather than a feature made me smile. I doubt anybody would take such a comment seriously, but I thought it created an opportunity to talk about it again. 

I’m pretty sure that Hitachi is the only vendor to offer it as GA. I’ve seen it and know that it works. Others talk about it but that’s about it (I understand they may be waiting for standards like TRIM). ZPR is a really great feature that allows you to reclaim unused capacity that can be used to offset future capacity purchases. Pretty good during times like these where purse strings are tightly controlled.

In the video I don’t even mention things like dynamic volume expansion or automatic dynamic relevelling etc. But put all of these together and Hitachi has a well stocked Dynamic Provisioning portfolio that stands up against any other vendors.

A few points about the video –

  • Yes that’s me – sorry I didn’t have a shave first.
  • Why a field of cows? Marc did his video in front of a field of cows so I thought it appropriate I respond like for like ;-)
  • Why two videos? It was shot as a single video but I’ve never done this before and at 14 minutes was too long for YouTube as a single video
  • Why don’t I work for HDS or HP or someone like that? Your guess is as good as mine. I do have to remind myself occasionally that I don’t actually work for HDS ;-)
  • Yes I know its a bit pants compared to Marcs many videos

Questions and comments always welcome.

I only ever talk about storage