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Message-ID: <7dbbaf60-c85d-5a7a-8f16-5f5e4ff43cd8@veeam.com>
Date:   Tue, 13 Jun 2023 12:47:29 +0200
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Subject: Re: [PATCH v4 11/11] blksnap: Kconfig and Makefile
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To:     Randy Dunlap <rdunlap@infradead.org>, <axboe@kernel.dk>,
        <hch@infradead.org>, <corbet@lwn.net>, <snitzer@kernel.org>
CC:     <viro@zeniv.linux.org.uk>, <brauner@kernel.org>,
        <willy@infradead.org>, <dlemoal@kernel.org>, <wsa@kernel.org>,
        <heikki.krogerus@linux.intel.com>, <ming.lei@redhat.com>,
        <gregkh@linuxfoundation.org>, <linux-block@vger.kernel.org>,
        <linux-doc@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <linux-fsdevel@vger.kernel.org>
References: <20230609115858.4737-1-sergei.shtepa@veeam.com>
 <20230609115858.4737-11-sergei.shtepa@veeam.com>
 <499ded51-3fb8-f11b-8776-08ab2e9a8812@infradead.org>
From:   Sergei Shtepa <sergei.shtepa@veeam.com>
In-Reply-To: <499ded51-3fb8-f11b-8776-08ab2e9a8812@infradead.org>
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On 6/13/23 01:43, Randy Dunlap wrote:
>> +config BLKSNAP
>> +	tristate "Block Devices Snapshots Module (blksnap)"
>> +	help
>> +	  Allow to create snapshots and track block changes for block devices.
>> +	  Designed for creating backups for simple block devices. Snapshots are
>> +	  temporary and are released then backup is completed. Change block
> 	                             when backup is completed.
> 
> or is the order of operations as listed: release snapshots and then backup
> can be completed?
> 
>> +	  tracking allows to create incremental or differential backups.

"when backup is completed." - it will be more correct.

Normal backup process:

Take snapshot                                        Release snapshot
    |    Start backup                        Finish backup   |
    |        |  Copy data from snapshot images    |          |
------------------------------------------------------------------------->
                                                                         t

In case of failure, for example, when the snapshot is overflowing:

                                           The snapshot is corrupted
Take snapshot                                   | Release snapshot
    |    Start backup                           |   | Finish failed backup
    |        |  Copy data from snapshot images  |   |    |
------------------------------------------------------------------------->
                                                                         t