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63 Posts
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1586
tdev page allocation deallocation
I am very much aware that as an when we write to tdev the pages will get allocated but what will happen if i delete half of data on that tdev ( or from the file system made up of those tdevs) will the pages get deallocate and come back to free pool space or it will not happen until we manually run the Pool Reblanace.
Also even if we unmask any luns from server , we need to destroy them to return the allocated storage back to free pool.
Kleanthis76
26 Posts
0
January 16th, 2013 23:00
Hi OnlySandy,
When a host writes to a TDEV then 768KB extents will be allocated as needed. So in your example you allocate some space and then you delete half of the space. The OS deletes the files on the inode list of the filesystem (f.e. when you delete files from an NTFS, Windows puts a $ as the first character) but does not zero out the "actual" data of the files. In order to reclaim the space from the storage , storage needs to find extents that contains only zeroes. So you need to to zero out the space that your data consumed. This is why you need the OS LVM to be able to do this. Such LVM is VxVM 5, VMware or with Win2K8 you can run storeclaim or sdelete.
Rebalance will move around extents to all the TDATs of your pool, to evenly balance the extents on the TDATs based on the Rebalance Variance.
Regards,
Kl.
sauravrohilla
859 Posts
1
January 15th, 2013 03:00
When you write data on tdev, it allocates tracks on the pool and when you delete it, it deletes the data but tracks will still be allocated.
You will need to run utility sdelete (on Windows server) followed by reclaim operation on storage to reclaim this space.
regards,
Saurabh
OnlySandy
63 Posts
0
January 16th, 2013 22:00
Thanks Saurabh . You are right . But that we need to run on host side.
Is there anything can be done on storage side without running any utility on host side to reclaim the storage tracks. Will pool rebalance on vmax can help with same ?
Zikas
278 Posts
0
January 16th, 2013 23:00
Hi Sandy,
try via SMC to select which devices you want to reclaim of to free up space.
Before Start the Reclaim or Free Space, if the devices are RDF's devices you have to split them.
Then start the procedure. Be carefull if you select an enormous amount of devices to reclaim or to free up space maybe it won't succeed.
Rebalancing will be done by the Storage side without your interfere.
This if you don't want to execute utilities on the host side.
As Saurabh said for Windows hosts you can execute the sdelete tool but you can use the StorClaim tool as well.
Also there is a tool for Linux in order to reclaim and free up space but i don't remember it now.
For HPUX hosts reclaim can be done if the hosts have Volume Manager 5.0 and later.
At version 4.1 and back you are not able to do reclaim.
sauravrohilla
859 Posts
0
January 17th, 2013 01:00
no, pool rebalance will not help you in this problem. Use host based utility (sdelete in case of Windows or Symantec Volume mangaer ) to write zeros on all deleted tracks.
regareds,
Saurabh Rohilla
OnlySandy
63 Posts
0
January 18th, 2013 03:00
OK understood. We need to fill those data blocks with ZERO's so that storage can reclaim those extents.
Now what's next . What is the command to reclaim the storage or do i need to destroy entire lun ? But in some cases where tdev is half way utilized we cant destroy also.
OnlySandy
63 Posts
0
January 18th, 2013 03:00
Just read below thread and understood the command to reclaim the free space.
https://community.emc.com/message/691848#691848
thanks everyone for their help