[gpfsug-discuss] Sub-block size not quite as expected on GPFS 5 filesystem?

[IBM Spectrum Scale]

In released GPFS, we only support one subblocks-per-fullblock in one file
system, like Sven mentioned that the subblocks-per-fullblock is derived by
the smallest block size of metadata and data pools, the smallest block size
decides the subblocks-per-fullblock and subblock size of all pools.

There's an enhancement plan to have pools with different block sizes and/or
subblocks-per-fullblock.

Thanks,
Yuan, Zheng Cai



From:	"Andrew Beattie" <abeattie at au1.ibm.com>
To:	gpfsug-discuss at spectrumscale.org
Date:	2018/08/02 09:10
Subject:	Re: [gpfsug-discuss] Sub-block size not quite as expected on
            GPFS 5 filesystem?
Sent by:	gpfsug-discuss-bounces at spectrumscale.org



Stephen,

Sorry your right, I had to go back and look up what we were doing for
metadata.

but we ended up with 1MB block for metadata and 8MB for data and a 32k
subblock based on the 1MB metadata block size, effectively a 256k subblock
for the Data


Andrew Beattie
Software Defined Storage  - IT Specialist
Phone: 614-2133-7927
E-mail: abeattie at au1.ibm.com


 ----- Original message -----
 From: Stephen Ulmer <ulmer at ulmer.org>
 Sent by: gpfsug-discuss-bounces at spectrumscale.org
 To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
 Cc:
 Subject: Re: [gpfsug-discuss] Sub-block size not quite as expected on GPFS
 5 filesystem?
 Date: Thu, Aug 2, 2018 11:00 AM



       On Aug 1, 2018, at 8:11 PM, Andrew Beattie <abeattie at au1.ibm.com>
       wrote:


 […]


       which is probably why 32k sub block was the default for so many
       years ....

 I may not be remembering correctly, but I thought the default block size
 was 256k, and the sub-block size was always fixed at 1/32nd of the block
 size — which only yields 32k sub-blocks for a 1MB block size.

 I also think there used to be something special about a 16k block size…
 but I haven’t slept well in about a week, so I might just be losing it.

 --
 Stephen

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