Stout Provisioning

13 02 2008

This is a copy of a question I’ve posed on the HDS forum. Highlights my sad state of mind, and that I can’t switch off when I’ve got a few days off for half term!

One of those odd questions that has been rattling around my brain recently has been about allocating pools for COW and Thin Provisioning. I’m anticipating trialling the former soon, and maybe the latter when I can get my hands on a USP-V.

I’m led to believe that the data is written to the pools in a very wide stripe, i.e. scattered all over it, sounding to me in a very similar fashion to the STK RVAs I was implementing in the mid to late 90s. So, the question is, what is the best practice for allocating the physical LDEVs that make up the pool, assuming Raid 5 7D+1P is the norm for the RGs? For a normal allocation to a host, I’d use a dispersed allocation, e.g. RG 1-1, 1-2, 1-3, 1-1, 1-2, 1-3, 1-1, 1-2, 1-3 in order, with a host based stripe on tape for good measure.

For a pool, would that still be best practice? Does the wide striping algorithm work in a similar fashion to a host based stripe, e.g. something that Veritas might do; or does it really matter?

Another thought in my head is about utilising thin provisioning pools to possibly enhance performance. My thought behind that is that you could use the principle of creating VDEVs across a large pool, but not over allocate the pool, so that you could have 3 layers of striping: a host stripe over a pool stripe over a physical stripe. I like to call that ‘Stout Provisioning’ (fans of Not the Nine O’Clock News will understand my meaning).

Could there be a benefit to that? Has anybody actually tried it? All opinions and experiences shared would be greatly appreciated.


No more virtual fubar

31 01 2008

To cut a long story short, my test data was ok. It was how Linux LVM handled the presented disks when I virtualised them, or to be more precise, the order in which they were presented. One of the tests I was doing was to see if it was important to re-advertise the disks after they were virtualised behind the NSC, so I had not presented them in the same order. When I re-virtualised the 9980 disks the third time, I presented them to the NSC in the same order as native to the linux host, and presented them as external Open-Vs. I presented them in that same order from the NSC to the Linux host, and Bob’s your relative, data was accessible and all was dandy. Brown trousers averted!

I then re-created the experiment from the USP-100 that I’m actually going to be migrating data from soon (before you jump up and down and shout ‘a USP to NSC/AMS – are you mad?’ – the answer to which is ‘occasionally’ – this is development data that should not have been there to start with). This time the presented disks are 14Gb Open-Vs, same size as formatted on the NSC and its production external storage on an AMS-1000. That worked a treat, and then I used shadowimage to replicate the data from the virtualised USP-100 through the NSC and out to the virtualised AMS, then re-presented that to the Linux host.

So there you have it. You don’t need to fork out for tiered storage manager (HDS – stop calling it TSM – it’s confusing, there’s already a TSM out there. I know it’s supposed to be called HTSM, with one of the characters in lower case, but everyone always forgets the ‘H’!) if you have a Shadowimage licence. You will need a couple of application outages to do a migration this way, but it can be done and timed to minimise the inconvenience to nothing.

Don’t forget the gotchas: present the old storage out as Open-Vs, and make sure your destination Open-Vs are the same size for Shadowimage to work; make sure you know whether or not the host O/S will need to have the virtualised old disks and subsequent new disks presented in the same order (probably not an issue with Veritas, for example); test, test and test again! I’ll be replicating my testing on AIX, Solaris and HP-UX, some with Veritas, others with native LVM. I’ll let you know how I get on.

Off to pick up the children now from nursery and after school clubs. Expensive business, childcare, and Gordon **** Brown just doesn’t help out enough with the tax breaks. It’s not so bad in the Midlands, but in London it cane cost £800 – £1000 per month for a child when the parents work full time, and a £55 / week tax break is a pathetic pittance. Oh how I wish he’d called that election a few months ago. Can’t wait to see him on the opposition benches. 

Life should be simple

27 01 2008

Just now I was chugging along with domestic life, masticating on the things on my mind, such as bill paying, feeding the family, making my code more efficient, when my 3 year old daughter nonchalantly ambles by wearing her Disney Princess dress that she got for Christmas and starts rummaging around her room. Then out she trots, happy as a pig in poop, because she’s found her tiara. I stop my thinking (I’ve been known to do that) and realise I’m jealous. Not of the tiara – it’s far too small for my large melon – but that life for her is so simple that her biggest worry is that she can’t find her tiara. I wish life could be that simple.

Talking of simple things, or things that should be simple, I’ve been lab testing array migration by externalising behind the NSC I look after. We already virtualise storage, but have never used it for migration. I recently emptied an old 9980 array, but that was by using host based mirroring. That work’s fine, but the problem is that I had to hand over the mirroring work to our Unix support team, who are so overwhelmed with work that it had to wait its turn. Perhaps being a control freak who does not like to have to rely on others to finish his work has something to do with it as well?

So now I’ve got the old 9980 to myself, I allocated a few LDEVs to my linux box, populated them with crud data, then decallocated it from the server and virtualised them behind the NSC. I’ve done this before in the lab with like for like storage, worked a treat. So I represent the now virtualised LDEVs back to the linus server, and it complains that the disk headers are fubar’d.

I de-virtualise (if there’s such a word) the storage and represent it native. Headers are still fubar’d. Oh dear. Going back through the process, I’m sure I didn’t cock up. I didn’t reformat the virtualised LDEVs. I did, however, present them from the NSC as Open-Vs, whereas on the 9980 they’re Open-Es. I did have the option of presenting them from the NSC as Open-Es, but I didn’t do that because a) I wasn’t expecting anything to be written to the 9980, and b) I wanted to try out using Shadowimage to migrate the data (I know there are other tools to do that, but they cost money). I’m going to redo this next week, this time I’ll virtualise as Open-Es and see what happens. This concerns me as I have seen other bloggers discuss how they’ve virtualised all sort of pre-existing data on a variety of arrays. Maybe I did cock something up? That’s the joy of testing I suppose. I’ve got to migrate data from a USP100 soon, so I’ll try some testing on that too. At least that should be like for like.

One final point before I head off with the family to the park – regarding my previous post, I’ve been asked how can a prospective employer contact me? Good point, seeing as I don’t publish my e-mail address (nothing personal, but I get enough spam). I moderate all posts that come in, so if you want to talk to me, just drop in a reply posting to this article. I’ll take the details, then delete the post so it won’t appear and will remain confidential. And please, no agents touting for CVs. More on that later…..

Been a while….

25 01 2008

It’s been a while since my last post. However, I have been getting lots of comments. Looking just now, it was around 35,000! Unfortunately, all spam. Another of life’s little irritations. I had to take down my union branch’s website forum recently because of spammers breaking through the defences. Went away for a two week holiday to Canada (lovely country, by the way) and found some of the site users most distressed at Viagra and various orifice probes being offerred as solutions to the questions they were posing.

I’ve been getting to grips more with our HDS kit recently. Tuning Manager is a bundle of laughs, isn’t it? As was pointed out to me, it was written in the Japanese market place, which is vendor driven rather than customer driven. Boy, does it show. And I enjoy some of their intuitive screens on Storage Navigator – who thought it was a bright idea when setting up Universal Replicator that right clicking on a large blank grey area of screen to get something done was intuitive?

On the domestic front, I’ve had to change the shower again. What is it with me and electric showers? They seem to last just long enough to be out of warranty and then *bang*. I’ve also been tracing my family tree, which has been really interesting, and at times my wife has had to suggest to me that I pause for a break, as she thinks I’ve been a tad obsessive with it at times. I think she may be right 🙂

I’ve got quite a lot of ranting to get out of my irritated system. And the odd question to pose. I’ll need to filter it out in small chunks.

Oh, and by the way, if anybody is looking for an experienced Storage professional to cover the Midlands area for a Professional Services Consultancy type role, let me know.