How can I check used space of snapshot-fs ?

[Lothar Krueler]

Hi there,
I want to use a snapshot-fs for Online-backup.
I created a S-fs, but I don't know how to check the space currently used for changed data. A bdf on the mounted s-fs shows me the used space of of the snapof-filesystem.
I don't want the s-fs to get out of space, but i also don't want to waste diskspace by using to much for s-fs.
Thanks in advance
Lothar

[Steve Steel]

Hi


look at

http://bizforums1-it1.mayfield.hp.com/cm/QuestionAnswer/1,,0x4cf9a12d6d27d5118fef0090279cd0f9,00.html

http://bizforums1-qa2.mayfield.hp.com/cm/QuestionAnswer/1,,0xb8a9d5fab40ed6118ff40090279cd0f9,00.html



Steve Steel

[Lothar Krueler]

Hi Steve, thanks for your response, but unfortunately I cannot access the links. (I tried yesterday an today).
I need a command for getting the currently used space on on mounted snapshot-filesystem only.
T.i.a.
Lothar

[Paula J Frazer-Campbell · Accepted solution]

Hi

This might help:-


http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0xb8a9d5fab40ed6118ff40090279cd0f9,00.html



Paula

[Steve Steel]

Hi


try
df -F vxfs -b

df -f vxfs -f

Report the total allocated block figures and the number of free
blocks, for all mounted file systems:


Steve Steel

[Lothar Krueler]

Thanks, I tried df
df -F vxfs -b
df -F vxfs -f
with and without pathnames
as you suggested, it always shows the same on the snapshot-filesystem and the original filesystem.
What's my fault ?
Lothar

[Lothar Krueler]

Ahhhh, I think got it:
I have to check space of both filessystems and
watch the difference. The difference is the currently used space (nearly ?) on the snapshot-fs.
Thanks.
Lothar

[A. Clay Stephenson]

Hi Lothar:

Using df to compare the original to the snapshot doesn't work either. The only thing that that can tell you is the amount of new files (actually the NET difference between the number of new files blocks created and the number of file blocks removed) in the original filesystem since the snapshot was taken. The real problem is that you have no way to know the number of blocks that have been updated. The first update of a given block uses one block of the snapshot buffer. Subsequent updates of that same block in the original filesystem do not use another snapshot buffer block.

The vxfs filesystems purchased directly from Veritas do have some utilities and df enhancement to display snapshot buffer usage but the HP OEM versions do not. It might be possible using adb to look at kernel structures but that is about the only way.

In practice, it is very unusual to require more than 20% of the size of the original filesystem for uses as a snapshot buffer and often as little as 5% will suffice. It depends upon the volatility of the data and the amount of time that the snapshot must remain in effect.

Food for thought, Clay

[Lothar Krueler]

Hi Clay,
seems that the questions isn't solved yet.
If i understand right, i have to guess. While using 20% there might be needed 5% only so i waste space, using 10% there might be needed 11% so the backup crashes. I want to keep unallocated space for raid 0/1 on my 12Hs most as possible. Please take a look at the attachment (arrayinfo.txt) and tell me, what you think how much space i can additionally allocate on my raids without loosing raid 0/1 capacity.
Thanks in advance, Lothar