SAN space calculations formatted->raw

[Sheldon Lee-Wen_1]

Hi everyone,

I was wondering if anyone knows where I can find information on SAN raw disk size requirements. I have a capacity requirement projection done (for formatted disk space) on my EVA5000 and I need to now calculate how much actual disk I will need. I know that I have to calculate OS filesystem overhead, RAID overhead and SAN overhead. If someone can point to the documentation on determining the SAN overhead (and AdvFS, NTFS and raid5 overhead) and how to calculate it I'd be very grateful.

Thanks,
Sheldon.

[Uwe Zessin]

Advfs and NTFS overhead, I don't know.

The EVA uses a 4D+1P formula for VRAID-5 - 10 GigaBytes of user space require 12.5 GigaBytes of "raw" disk space (that is SWGB).

You need to understand the difference between "hardware" and "software" GigaBytes. HWGB is what the vendors specify. It is a base 10 value. The EVA displays SWGB which is base 2.

Example:
A "146GB" disk drive shows as "136.73GB" on the EVA:
146000000000.0/1024/1024/1024 = 135.97

Well, it does not fit exactly, because that disk has a bit more than 146,000,000,000 bytes.

--

Next thing is "protection capacity". The EVA does not use traditional "spare disks" - it includes them into the disk group so they can be used for user I/Os, too. Their capacity is equally distributed over all disks in the disk group. For level=1, calculate 2 time the size of the larges disk in the group (you normally only put equally sized disks in a group).

--

You need to reserve some room for meta data overhead - about 0.2% and you should not fill a disk group completely, most users stay less than 95%.

[Vincent Fleming]

Sheldon,

If you tell me how much formatted capacity you want, I can generate an estimate for you.

Please specify drive size (73GB, 146GB, 300GB, or 250GB FATA), vRAID level, number of "spares" (see Uwe's description of these), and indicate if you need full redundancy (it's configurable). If you are putting this in an existing EVA, please note what model.

Thanks,

Vince

[Sheldon Lee-Wen_1]

Hi Vincent,

I have a spreadsheet over 10 years, do you have an email address I can send a sanitized version to and we can discuss from there?

Thanks,
Sheldon.

[Vincent Fleming]

vincent.fleming@hp.com

[Policia]

could I get this this emailed to me as well.
rxkern@gmail.com

[Louis Henninger_1]

Hi all:

If I'm not mistaken, HP has a tool you can download that will tell you exactly how many disks to use to have a formatted space of "x".
It works for EVA, MSA and I think XP (I've only used it for MSA and EVAs.

You should also be concerned with what the space will be used for (Exchange, SQL or other databases). Some applications perform better with more disks of a smaller size, than largest disks and fewer of them.

Regards,

Louis

[Policia]

I have been using the HP Sizing tool found in the link posted above. I find that the Sizing tool is incorrect. Any thoughts?