Max usable capacity of XP10k

[Victor Sien]

Hi,

If we populate an XP10k to its max number of drives of 240 using 300GB, we get 72TB of raw space. how much of that is actually useable.. an hp rep once mentioned only 50tb is usable, is taht true? why?

[TTr]

According to

http://h18006.www1.hp.com/products/storageworks/xp10000/specs.html

The maximum raw capacity is 95TB and max usable is 83TB. (400GB FC drives are available)

The usable capacity depends on the RAID type and the number of disks that you put in each array group.

[Victor Sien]

Hi,

thansk for the reply. assuming thats correct - 83TB out of raw capacity of 95TB - how was the assumption made? What raid level and emulation was used to come up with teh figure? appreciate any comments.. im trying to figure out the numbers thrown at me by our storage guy (and im not) as i size the application.. thanks a lot.

[TTr]

To get the 83TB usable obviously the RAID type that was used is the one that uses the most data disks and the fewer (1) parity disks.

Looking at the possible RAID types, RAID5 with 7d+1P, 14D+2P, 28D+4P, they all have they have 1/8 parity disk overhead. So 1/8 of 95TB is about 12TB and that is the parity overhead.

Also you have to account for spare drives but in these calculations, they assume the minimum number of hot spares which is 1.

[TTr · Accepted solution]

> im trying to figure out the numbers thrown at me by our storage guy

Don't get too upset if his numbers are much smaller. The 83TB is the maximum possible. Usually you get much less than that because you can have up to 16 spare drives (the spare drives are unused drives sitting there in case one of the RAIDed drives fails) and you may have RAID1 groups which have 50% parity (mirroring) overhead.

There is also additional overhead when the space is allocated to servers.

You would need detailed array layout to verify the numbers.

[Victor Sien]

Thanks Tt.. That was so helpful.. with that, i figured out they were using raid 6D+2p (75% efficiency) and 16 spare drives.. which explains why he said approx. 50tb out of 72tb.

thanks!

[DCh_2]

> i figured out they were using raid 6D+2p (75% efficiency) and 16 spare drives

Was this confirmed by you storage guy? You could still end up with 75% efficiency with the right mix of RAID1 and RAID5 groups.

Also 6D+2P is mostly used with extremely critical data.

[Haggisnneeps2]

How dow the XP10000 overcome the 2TB SCSI limitations imposed on every other SCSI storage device out there?