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List:       evms-devel
Subject:    [Evms-devel] [ evms-Feature Requests-1795959 ] incremental snapshots
From:       "SourceForge.net" <noreply () sourceforge ! net>
Date:       2007-09-17 1:35:32
Message-ID: E1IX5WO-0008DO-F4 () sc8-sf-web24 ! sourceforge ! net
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Feature Requests item #1795959, was opened at 2007-09-17 01:35
Message generated for change (Tracker Item Submitted) made by Item Submitter
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=383345&aid=1795959&group_id=25076

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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Sergey Ivanov (sergey57)
Assigned to: Nobody/Anonymous (nobody)
Summary: incremental snapshots

Initial Comment:
It should be very good to have read-only snapshots like in Solaris' ZFS, with some \
tool to send/receive them. If I have evms volume v1, I can create and activate first \
snapshot of this volume, say v1.1. Now I can dump this volume with dd to have offline \
snapshot, which may be restored. Sure, dd will copy all space of the volume including \
unused, which is sad. Much better if special utility will skip these zeroes.  But \
then, say after a day, I want to create second snapshot, v1.2. Then I want to "dump" \
incremental dump, the difference between v1.1 and v1.2, and save it as an  a kind of \
incremental backup. So that original volume if crashed may be restored to state at \
the moment of activating v1-2 by restoring it from v1-1 dump and then applying this \
incremental dump v1.2-v1.1  in ZFS terminology it's like:
---
zfs snapshot v1@1
zfs send v1@1 > /backups/v1.1
---
Then, after a day:
---
zfs snapshot v1@2
zfs send -i v1@1 v1@2 > /backups/v1.2-1
---
And v1 may be restored after being destroyed by:
---
zfs receive vRestored </backups/v1.1
zfs receive vRestored </backups/v1.2-1
---
Because evms have all the track of modified blocks between volume and it's snapshot, \
it can be a great improvement over existing technologies of incremental
backups, which usually involve scanning all files or at least directories on the \
volume, that can be a huge  task for, for example, imap storage.
--
  Sergey Ivanov. 

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