[lustre-discuss] Data migration from one OST to anther

Tung-Han Hsieh thhsieh at twcp1.phys.ntu.edu.tw
Sun Mar 3 02:00:17 PST 2019

Dear All,

We have a problem of data migration from one OST two another.

We have installed Lustre-2.5.3 on the MDS and OSS servers, and Lustre-2.8
on the clients. We want to migrate some data from one OST to another in
order to re-balance the data occupation among OSTs. In the beginning we
follow the old method (i.e., method found in Lustre-1.8.X manuals) for
the data migration. Suppose we have two OSTs:

root at client# /opt/lustre/bin/lfs df
UUID                   1K-blocks        Used   Available Use% Mounted on
chome-OST0028_UUID    7692938224  7246709148    55450156  99% /work[OST:40]
chome-OST002a_UUID   14640306852  7094037956  6813847024  51% /work[OST:42]

and we want to migrate data from chome-OST0028_UUID to chome-OST002a_UUID.
Our procedures are:

1. We deactivate chome-OST0028_UUID:
   root at mds# echo 0 > /opt/lustre/fs/osc/chome-OST0028-osc-MDT0000/active

2. We find all files located in chome-OST0028_UUID:
   root at client# /opt/lustre/bin/lfs find --obd chome-OST0028_UUID /work > list

3. In each file listed in the file "list", we did:

	cp -a <file> <file>.tmp
	mv <file>.tmp <file>

During the migration, we really saw that more and more data written into
chome-OST002a_UUID. But we did not see any disk release in chome-OST0028_UUID.
In Lustre-1.8.X, doing this way we did saw that chome-OST002a_UUID has
more data coming in, and chome-OST0028_UUID has more and more free space.

It looks like that the data files referenced by MDT have copied to
chome-OST002a_UUID, but the junks still remain in chome-OST0028_UUID.
Even though we activate chome-OST0028_UUID after migration, the situation
is still the same:

root at mds# echo 1 > /opt/lustre/fs/osc/chome-OST0028-osc-MDT0000/active

Is there any way to cure this problem ?

Thanks very much.


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