Fractional reserve once again

[saranraj456]

Hi Frndz,

I knew Fractional reserve is a Buzz word and I apprehended the term after the reading this document.Can you please help me in clarifying the below two points

1.Fractional reserve will normally reserve the space in the contained volume,if the volume space reservation is set to none it won't reserve the space for that volume in the aggregate.Then how it's possible for the fractional reserve to reserve the space to LUN overwrite.?

2.For an example if i create a volume of 100 GB with fractional reserve 100%, i have created a LUN for 80GB in that and i used snap reserve 20 % to that volume.Now the volume is fully occupied,if the LUN gets filled up, is it feasible to use the fractional reserve space and protect the upcoming write request?

Thanks,Saran

[scottgelb]

Usually san users will use space reservation or fractional reservation but not both... often both are set to zero now and then the volume is sized over the lun size to handle the estimated snapshot space, then snapshot autodelete and volume autogrow are used to ensure the lun doesn't run out of room.  "df -r" is useful to see space reservation effect and the space reserve isn't seen until the first snapshot is taken.  And with VMware most are using thin provisionied luns so the dedup space goes back to the volume or aggregate (if the lun is reserved no space is saved on the lun).

Rick Joos has a really good paper and Steve Botkin a really good preso (I think the one you are talking about) that explains reservation really well.. It can take 2 reads sometimes then it makes more sense (I still review them every so often).

[saranraj456]

Scott,

Can you please provide me the link for that paper..

Regards,
Saran

[scottgelb]

TR-3483 http://www.netapp.com/us/library/technical-reports.html

[saranraj456]

Scott,

if we use both FR and space reservation in a volume .Will that make any specific use?

Regards,saran

[scottgelb]

Fractional reserve is based on space reserve. At 100 percent default or lower to reserve less space. They work together. At zero there is no reserve.

[saranraj456]

HI Scott,

Please clarify  the comment stated above,Usually san users will use space reservation or fractional reservation but not both..

Regards,
Saran

Scott Gelb wrote:
Fractional reserve is based on space reserve. At 100 percent default or lower to reserve less space. They work together. At zero there is no reserve. 

[scottgelb]

Typo On my part. I meant snap reserve or space reserve. Fract reserve and space reserve go hand in hand. I mixed the names

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