[Bugs] [Bug 1471753] New: [disperse] Keep stripe in in-memory cache for the non aligned write
bugzilla at redhat.com
bugzilla at redhat.com
Mon Jul 17 11:56:33 UTC 2017
https://bugzilla.redhat.com/show_bug.cgi?id=1471753
Bug ID: 1471753
Summary: [disperse] Keep stripe in in-memory cache for the non
aligned write
Product: GlusterFS
Version: mainline
Component: disperse
Assignee: bugs at gluster.org
Reporter: aspandey at redhat.com
CC: bugs at gluster.org
Description of problem:
Problem:
Consider an EC volume with configuration 4 + 2.
The stripe size for this would be 512 * 4 = 2048.
That means, 2048 bytes of user data stored in one
stripe. Let's say 2048 + 512 = 2560 bytes are
already written on this volume. 512 Bytes would
be in second stripe. Now, if there are sequential
writes with offset 2560 and of size 1 Byte, we have
to read the whole stripe, encode it with 1 Byte and
then again have to write it back. Next, write with
offset 2561 and size of 1 Byte will again
READ-MODIFY-WRITE the whole stripe. This is causing
bad performance because of lots of READ request
travelling over the network.
There are some tools and scenario's where such kind
of load is coming and users are not aware of that.
Example: fio and zip
Solution:
One possible solution to deal with this issue is to
keep last stripe in memory. This way, we need not to
read it again and we can save READ fop going over the
network. Considering the above example, we have to
keep last 2048 bytes (maximum) in memory per file.
Version-Release number of selected component (if applicable):
How reproducible:
Steps to Reproduce:
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Actual results:
Expected results:
Additional info:
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