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From: Zdenek Kabelac <zkabelac@redhat.com>
To: lilofile <lilofile@aliyun.com>,
	device-mapper development <dm-devel@redhat.com>,
	Mike Snitzer <snitzer@redhat.com>
Cc: Ondrej Kozina <okozina@redhat.com>, axboe <axboe@kernel.dk>,
	Edward Thornber <thornber@redhat.com>
Subject: Re: dm-thin
Date: Tue, 21 Oct 2014 11:32:54 +0200	[thread overview]
Message-ID: <54462846.7040502@redhat.com> (raw)
In-Reply-To: <20b42a29-27ce-4395-9cd9-843f2acfcab2@aliyun.com>

Dne 21.10.2014 v 03:36 lilofile napsal(a):
> In dm-thin.c,
> /*
>   * The block size of the device holding pool data must be
>   * between 64KB and 1GB.
>   */
> #define DATA_DEV_BLOCK_SIZE_MIN_SECTORS (64 * 1024 >> SECTOR_SHIFT)
> #define DATA_DEV_BLOCK_SIZE_MAX_SECTORS (1024 * 1024 * 1024 >> SECTOR_SHIFT)
>
> why the block size must be between 64KB and 1GB, can I change  the value of DATA_DEV_BLOCK_SIZE_MIN_SECTORS? what effect  if the value of DATA_DEV_BLOCK_SIZE_MIN_SECTORS<128?


Performance reasons mainly - updating metadata much more frequently is 
lowering the throughput considerable.

The other issue is you would also scale up required metadata size.

Zdenek

      reply	other threads:[~2014-10-21  9:32 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-10-13 15:27 A patchset to limit the number of outstanding bios Mikulas Patocka
2014-10-13 16:03 ` Joe Thornber
2014-10-13 16:20 ` Mike Snitzer
2014-10-13 20:52   ` Mikulas Patocka
2014-10-15 12:12   ` device-mapper lilofile
2014-10-21  1:36   ` dm-thin lilofile
2014-10-21  9:32     ` Zdenek Kabelac [this message]

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