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Ecco perchè Compellent ti propone meno dischi

Sono dispiaciuto di leggere post come questi.

Probabilmente, come per sua stessa ammisione, chi scrive quel blog non conosce molto bene lo storage Compellent e magari c’è bisogno di una spiegazione per capire meglio come è possibile raggiungere certi risultati.

Vorrei dire innanzitutto che non conosco l’ambiente di questa particolare trattativa/progetto, ma sono un rivenditore Compellent e lavoro ogni giorno per configurare sistemi.

Prima di tutto noi usiamo il 99mo percentile (come suggerito da Compellent) e non il 95mo. In più consideriamo 177 IOPS e non 220 IOPS per i dischi a 15000 Giri. Utilizziamo inoltre documenti Compellent interni per fare delle configurazioni adeguate. Compellent è davvero (quasi troppo) pignola nella raccolta dei dati del cliente (iops, spazio, latenze, n. di server coinvolti, tipo di carico…etc), quindi mi sembra strano quello che hai scritto.

Compellent, diversamente da NetApp, fornisce Fast Track, Data Progression e Dynamic Block Cache, queste funzionalità aiutano ad ottenere una maggiore performance con un minore impiego di risorse rispetto ai concorrenti. Utilizzandole assieme è possibile raggiungere numeri davvero impressionanti!

Seguimi in questi calcoli: 11 dischi attivi (supponendo che un cassetto con 12 dischi ne abbia uno di spare), raggiungono circa 2000 IOPS ma:

Fast Track

è la capacità di scrivere dati sulla porzione più veloce dei dischi (tracce esterne, circa il 20% dello spazio disco) e ottenere più IOPS e meno latenza.

Se puoi scrivere/leggere dati sulle tracce esterne puoi guadagnare, in pratica, qualcosa come il 15/30% di miglioramento delle performance con una notevole diminuzione della latenza dei tuoi dischi (l’effettivo vantaggio dipende dal numero di server e dalla dispersione delle scritture).

In questo caso Il nuovo totale sarebbe di 2000+20% = 2400 IOPS. ;)

Data Progression

è l’automated tiered storage (non importa cosa tu o la tua compagnia ne pensi ma, se ben implementato, permette un notevole vantaggio). Data Progression, grazie a Fast Track, può lavorare anche su un solo tipo di dischi!

Quindi puoi scrivere dati in Raid10 sulle tracce più veloci e poi farli migrare, secondo politiche e profili, verso Raid5/6 in altre parti del disco.

Con altri produttori devi scegliere in anticipo il tipo di Raid (Raid5 o 6 per risparmiare spazio, Raid10 per avere migliori performance, ma non entrambe sullo stesso volume!).

Non aumentiamo in questo modo le IOPS ma, di sicuro, non le peggioriamo per effetto della scelta di un particolare Raid.

Dynamic Block Cache

La cache di Compellent è piccola (512MB per le scritture in mirror e 3GB a controller per le letture) ma è davvero flessibile e intelligente!

Per ogni LUN puoi scegliere il comportamento della cache e la grandezza del blocco varia dinamicamente tra 2KB e 256KB, significa che il controller alloca lo spazio necessario e non uno prefissato. Nel mondo reale significa che hai più spazio e flessibilità nel gestire i flussi I/O rispetto all’utilizzo di blocchi prefissati.

Spero di aver chiarito al meglio perchè Compellent propone meno dischi dei concorrenti nella maggior parte dei casi.

Why Compellent proposes fewer disks

Dimitris,

Sorry to see blog posts like this one.

I like your blog and often I read it but, this time I think you have done wrong calculations and the result isn’t very good.

Probably, as per admission, you don’t know very well Compellent’s stuff and you need some help to better understand how it is possible to achieve similar results.

I would like to say in advance that I don’t know this particular deal/customer environment but I’m a Compellent reseller and I work every day to configure systems.

First of all I use 99th and not 95th percentile (Compellent suggests it to me), second I use 177 IOPS per second and not 220 IOPS per second on 15K rpm disks. We are using internal Compellent documents to do the right sizing to be sure to do the right configurations. Compellent is very, very, very – sometimes too picky- in customers data collections (iops, space, latencies, # of servers involved, type of workload and so on) so it seems very strange to me what you are writing.

Compellent, opposed to NetApp, has Fast Track, Data Progression and dynamic block cache and those help to achieve more performance with less resources than competitors, these features works all together to deliver, some time, awesome numbers!

Follow me with my calculations: 11 active disks (I suppose that 12 disks tray means 1 spare) deliver near 2000 raw IOPS but:

Fast Track

it is the ability to write data on the fastest portion of the disk (external tracks, about 20% of the disk space) and obtain more IOPS and less latency (NetApp hasn’t this feature).

If you can read/write data on external tracks you will gain, in practice, something like 15/30% of better performance and very low latencies from your disks (the advantage depends by number of servers and dispersion of writes).

the new total is 2000+20% = 2400 IOPS. ;-)

DataProgression

It is automated tiered storage (its not important what you or your company think about it but, if it is well implemented, it gives very useful advantages). Data Progression works on a single tier of disks too also thanks to Fast Track!

So you can write data in RAID10 on Fastest tracks and then they will be migrated according to policies/profiles to RAID5/6 in other portions of disks.

With NetApp you need to choose in advance the type of RAID (RAID 4 or DP to save space or RAID10 to have better performance, but not all on the same volume!).

We don’t add more IOPS here but there aren’t constraints and less performance due to the use of a certain raid!

Dynamic Block Cache

Compellent’s cache is small (512 MB for mirrored writes and 3GB per controller for reads) but it is very flexible and auto tuned! (BTW, I don’t know the NetApp proposition for the deal you speak about, but if it is a FAS 2040 we are speaking of similar amounts of cache).

You can choose for each LUN the cache behavior and the block is dynamic from 2KB to 256KB, it means that the controller allocates the right space needed and not prefixed blocks. In real world it means that you have more space and flexibility if compared to fixed blocks to manage IO peaks.

I hope I cleared at best why Compellent is proposing less disks than competitors in most of cases.

Doubts, questions or comments? Let me know.

ciao,

Enrico


The best space guarantee program

After NetApp and Pillar,  3Par and HDS have now their “space guarantee” programs, but not EMC!

In the last days I saw a lot of chattering about this argument from many sources (you can find some links here, here, here and one from EMC here).

Space guarantee programs are only marketing campaigns to lure customers with fireworks and not with real substance.

Some of these programs have a lot of fine prints and clauses that look like this: “…The 50 percent guarantee is for the raw storage capacity for migrating from third party RAID-1 source environments to dynamically provisioned RAID-5 target environments. For any third party RAID-5 environment, Hitachi Data Systems will guarantee a 20 percent storage capacity reduction. …” :-D  (here the complete press-release from HDS).

So if you migrate your DB LUNs from RAID1 to RAID5 thin provisioned you can save space but no guarantees about performance! it seems more a well packaged and legalized fraud than a real opportunity for the customers!

Now I would like to show how my space (and performance) guarantee program works, a recent success case with Compellent.

My Space (and performance) guarantee program:

Compellent Storage Center with its Automated tiered storage (Data Progression), Thin provisioning (Dynamic capacity), space and performance efficient snapshot (instant replays) features may save you a lot of space, grant IOPS and big savings without any more or less hidden clause.

One of our Compellent’s customers (SCM Group) acquired their first Compellent Storage Center more than one year ago and they migrated some of their data to it, one year after (it took quite a bit to test the whole solution in production about support, real different workload, management, etc.) they then decided to move all their contents from an old HDS AMS 500  to Compellent!

The HDS was configured with a total of 1 controllers tray + 8 disk trays as follow:

  • 2 trays  300GB/10K : 6.6TB allocable capacity;
  • 4 trays 146GB/10K : 6.5TB allocable capacity;
  • 3 trays 146GB/15K : 4.9TB allocable capcity;

All the disks were configured in RAID5 (6D+1P, 1 spare per tray).

TOTALS

  • RAW disks capacity (excluding spares) is about 21TB;
  • Theoretical allocable capacity was 18TBs;
  • Really allocated for usage was 14TBs, due to shadow images (LUN clones);
  • Really used was 12,5TB!!! (near an half of raw);

We did a complete analysis of their needs and summarized the findings in these two following graphs (click on pictures for a full size view):

iops

iops

spazio

spazio

You can easily draw two important conclusions:

  1. The space used is high: nearly 80% of usable space;
  2. The real iops deliverd are not a lot (99th percentile is 4059): no wide striping.

Well, with these information and forecasted growth in our mind we designed the best solution for the customer (not on the basis of a unrealistic marketing program):

The results are the following:

  • 135 FC disks were replaced by only 38 300GB/15K FC DISKS: less than one third!
  • To achieve new space requirements (present + 30% forecast growth) we added 16 1TB/SATA disks!
  • + 7000 measured IOPS from the Compellent upgraded (thanks to fast track and data progression), + 72% than HDS!
  • 22.7TB of allocable space, much more usable than what was allocated on HDS, thank to Instant Replays!
  • The Array is SSD ready (added more backend loops and some slots are free to accomodate some SSD disks in near future)!
  • Space usage down to 12 Rack Units from 27!
  • Huge energy savings (4 trays compared to 8 trays + 1 controller), something like 6KW (including cooling)!

And last, but not least: if we break up the cost the customer had to face for the whole operation into what covered the same space/performance they already had and what covered the increase in space/performance, well, the first part was the very same needed to just sustain the old storage (maintenance + power/cooling dissavings), all in all what they payed more for was only what they got more!

This is the best NON Marketing space (and IOPS) guarantee program I know, what do you think about it?

ES

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