Thank you Vasily and Simon for the clarification!
I was looking further into it, and I got stuck with more questions :)
- In
https://www.ibm.com/support/knowledgecenter/STXKQY_5.0.0/com.ibm.spectrum.scale.v5r00.doc/bl1adv_hawc_tuning.htm
I read:
HAWC does not change the following behaviors:
write behavior of small files when the data is placed in the
inode itself
write behavior of directory blocks or other metadata
I wondered why? Is the metadata not logged in the (same) recovery logs?
(It seemed by reading
https://www.ibm.com/support/knowledgecenter/en/STXKQY_4.2.0/com.ibm.spectrum.scale.v4r2.ins.doc/bl1ins_logfile.htm
it does )
- Would there be a way to estimate how much of the write requests on a
running cluster would benefit from enabling HAWC ?
Thanks again!
Kenneth
On 31/08/18 19:49, Vasily Tarasov wrote:
That is correct. The blocks of each recovery log are striped across
the devices in the system.log pool (if it is defined). As a result,
even when all clients have a local device in the system.log pool, many
writes to the recovery log will go to remote devices. For a client
that lacks a local device in the system.log pool, log writes will
always be remote.
Notice, that typically in such a setup you would enable log
replication for HA. Otherwise, if a single client fails (and its
recover log is lost) the whole cluster fails as there is no log to
recover FS to consistent state. Therefore, at least one remote write
is essential.
HTH,
--
Vasily Tarasov,
Research Staff Member,
Storage Systems Research,
IBM Research - Almaden
----- Original message -----
From: Kenneth Waegeman <[email protected]>
Sent by: [email protected]
To: gpfsug main discussion list <[email protected]>
Cc:
Subject: [gpfsug-discuss] system.log pool on client nodes for HAWC
Date: Tue, Aug 28, 2018 5:31 AM
Hi all,
I was looking into HAWC , using the 'distributed fast storage in
client
nodes' method (
https://www.ibm.com/support/knowledgecenter/en/STXKQY_5.0.0/com.ibm.spectrum.scale.v5r00.doc/bl1adv_hawc_using.htm
)
This is achieved by putting a local device on the clients in the
system.log pool. Reading another article
(https://www.ibm.com/support/knowledgecenter/STXKQY_5.0.0/com.ibm.spectrum.scale.v5r00.doc/bl1adv_syslogpool.htm
) this would now be used for ALL File system recovery logs.
Does this mean that if you have a (small) subset of clients with fast
local devices added in the system.log pool, all other clients will use
these too instead of the central system pool?
Thank you!
Kenneth
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