MSA20 logical drive overhead

[Dmitri Smirnov]

I'm trying to setup a new MSA20 with 12 x 250GB SATA drives connected to 6402 controller.

Question: looks like I'm losing about 10% of overall capacity on RAID-0 with different number of drives in logical drive. It is around 200-300 GB with RAID-0 and 500GB with RAID-5.

Is it a normal feature of MSA-20 and can I save this space somehow?

[Jefferson Humber]

You shouldn't loose any space really with RAID0 (striping), but you will loose 1 HDD's worth of space with RAID5... since one disk becomes the parity disk.

I would seriously not even consider RAID0 unless you can afford to loose all of your data !

One thing to remember is the actuall size of the useable space on the drive is not 250Gb, this is a marketing ploy. The actually space of the drive is slightly less than this. It's got something to do with a Gb is actually 1024Mb, and not 1000Mb (which HDD manufacturers seem to use).

[Dmitri Smirnov]

Wow, I'm more confused now.

250,000,000/1024/1024 = 238.41

Does it mean that 'hpacucli' reports disk size in 'marketing' bytes and logical drive size in 'technical' bytes?

=> controller serialnumber=P9B280DMQRM02U physicaldrive 1:3 show


MSA20 at E039MLJ14R
physicaldrive 1:3
Box: 1
Bay: 3
Status: OK
Drive Type: Data Drive
Interface Type: SATA
Size: 250 GB
Firmware Revision: YAR511W0
serialnumber: Y69HAXTE

=>controller serialnumber=P9B280DMQRM02U create type=ld drives=1:3 raid=0

=> controller serialnumber=P9B280DMQRM02U logicaldrive 1 show


MSA20 at E039MLJ14R
logicaldrive 1
Size: 232 GB
Fault Tolerance: RAID 0
Heads: 255
Sectors per Track: 32
Cylinders: 59844
Stripe Size: 128 KB
Status: Ok
Array Accelerator: Enabled
Preferred Controller Chassis Slot: 1

[generic_1]

There is going to be some overhead for the array as well as the OS for all the pointers and raid setup junk. As well as the 21" monitor syndrome vs your 250GB disk LOL. This is normal.