VA7400 , DS2405 - Disk Management

[Deepak Seth_1]

We recently bought VA7400 and a 2405 Disk Enclouser - fully populated . That means total of 30 Disk * 75 Gig = 2250 Gigs. That what was our requirement .
But after installting it and start using it , we figure out that , it reserve 2 Disk for hot spares , 4 for Redudancy ( i think for stripping) and some how 75 gig disk become just 65 usuable . So now we were left with around 1450 gig of usuable space. This is how my calculation looks like


Redundancy 375
Hot Spares 200
System 1 164
System 2 722
System 3 380


We are plannig to buy another enclouser of DS2405 ( 15 drives , either 75 gigs or 146 gigs) . Can u guys tell me what is formula to find out how much disk space we get from DS2404 (let say by using 75 gig disk drives) . Do we need to use Hot Spares for each disk enclouser ? What about Redundancy ?

[Steve Bardell]

You can usually assume that the last 5 disks in the array when fully populated will not be actual storage, but reserved for things like striping and hotspares. My strong recommendation is to figure out how much space you actually need, and buy 50% more. This may become costly, but its a good rule of thumb when trying to avoid running out of space.

go to www.on-queue.com and search on A6250A and A6194A, someone should be able to help you get what you need.

Best of luck
Steve B
On Queue

[Marco Hogeveen]

You could win a little more diskspace if you set the hotspare configuration from Auto to 1, that means: 1 (largest)disksize per Redundancy Group will be used as hotspare, when it's on Auto it will use 2 disks if you have more then 15 disks in your Redundancy Group.

If you add another DS2405 with 15 73 GB drives (so 45* 73 GB total) and 1 hotspare per RG and RAID setting to Autoraid you will have: 1289 GB available in RG1 and 1112 GB available in RG2 so a total of 2401 GB.

I do not think you can use 146 GB drives on a VA7400.

Hope this helps.

Marco

[Karsten_4 · Accepted solution]

Hi

the Formula for the VA 74x0 is :

(Total Disks - 2x(Spare Disk Level + 2(for Autoraid)) x Size x 0,9

in your Example :
(30 - 2x( 2 + 2 )) x 73 GB x 0,9 = 1445 GB

of course you can also use only one Spare Disk per red. Group (whitch is save):
(30 - 2x (1 + 2 )) x 73 GB x 0,9 = 1576 GB

and whith only a little more Risk (no Hot Spare Disks):
(30 - 2x (0 + 2 )) x 73 GB x 0,9 = 1708 GB

Compared whith other Array (EVA or the EMCs) you have a very good ratio between Brutto and Netto. And whith 45 Drives the Ratio gets even better and the Performance of the Array is higher.
(45 - 2x (1 + 2)) x 73 GB x 0,9 = 2562 GB

Please keep in Mind that this are "Marketing" Gigabytes (1000^3) and not real Gigabytes (1024^3).
There are no 75 GB Disks, they are 73GB.

[Deepak Seth_1]

How you have arrived at 0.9 ? Is it something to do with parity(Raid5) . How can i change my spare from 2 to 1 per redudancy group ? Also after formating the disk of 73 gig , it become just 65 gig usuable . i think it is realted to block size and therefore drive size shriks ?

[Karsten_4]

Hi

The VA uses Autoraid : this means Data is stored in Raid 0/1 and Raid 5DP (Double Parity). Data is moved between both Raid Levels, depending on the usage. (often used Data is kept in RAID 0/1 (for Performance) and the rest in RAID 5DP (cheap). When the Array is full, there can be max. 90% Data in RAID 5DP and min. 10% in RAID 0/1. So you see : 0,9 is an Correction Faktor to address this (an other things, for example : you loose add. 2% for lowlevel Parity (520 Byte per Sector vs. 512 Byte)).
So : adding a 73GB HDD x 0,9 = 66 GB Netto more Space in the Array useable for LUNs.

There is no RAID5 in the VA. (only RAID 0/1 and RAID 5DP)

To change the Hot Spare Level you can use the GUI (Command View) or the CLUI. It is now set to automatic and you should set it to 1 (for 30-45 HDDs). There is no need to reboot. The Settings come effective in few seconds.