Re: A cache tier issue with rate only at 20MB/s when data move from cold pool to hot pool

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On 06/16/2015 01:17 PM, Kenneth Waegeman wrote:
Hi!

We also see this at our site:  When we cat a large file from cephfs to
/dev/null, we get about 10MB/s data transfer.  I also do not see a
system resource bottleneck.
Our cluster consists of 14 servers with each 16 disks, together forming
a EC coded pool. We also have 2SSDs per server for the cache. Running
0.94.1
Hi,

Does someone has an idea about this? Is there some debugging or testing we can do to find the problem here?

Thank you!

Kenneth



So we are having the same question.

Our cache pool is in writeback mode, can it help to set it in readonly
for this?

Kenneth

On 06/16/2015 12:58 PM, liukai wrote:
Hi all,
   A cache tier, 2 hot node with 8 ssd osd, and 2 cold node with 24 sata
osd.

   The public network rate is 10000Mb/s and cluster network rate is
1000Mb/s.

   Using fuse-client to access the files.
The issue is:

   When the files are in hot pool, the copy rate is very fash.

   But when the files are only in cold pool, the rate only reach 20MB/s.

   I known that when files are not in the hot pool, the files should
been copy from cold pool to hot pool first, and then from hot pool to
client.

   But the cpu, ram and network seems not the bottleneck. and will be
the cause of system design?

   Are there some params to adjust to improve the rate from cold pool to
hot pool?

Thanks
2015-06-16
------------------------------------------------------------------------
liukai


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