From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kyle Hayes MIME-Version: 1.0 Message-Id: <01110208435117.08803@khayes-lin> Content-Transfer-Encoding: 8bit Subject: [linux-lvm] snapshot questions Sender: linux-lvm-admin@sistina.com Errors-To: linux-lvm-admin@sistina.com Reply-To: linux-lvm@sistina.com List-Help: List-Post: List-Subscribe: , List-Unsubscribe: , List-Archive: Date: Fri Nov 2 10:42:03 2001 List-Id: Content-Type: text/plain; charset="us-ascii" To: linux-lvm@sistina.com We are considering using LVM to do database snapshots for backups. I have some questions that the HOWTO's etc. do not seem to answer. My largest concerns are that we will end up with a read-only corrupt filesystem. This seems to be a problem reported in the mailing lists. 1) how does the snapshot actually work? My understanding is that the creation of a snapshot partition sets up a new LV on the same VG as the "source" partition. This new partition is then used for writes to the "source" partition. When the snapshot LV is removed, do I get a disk IO hit as these changes are copied back to the "source" partition? Or, does it work more like Veritas where the changed data go to the "source" and the original values are copied to the snapshot partition? The Veritas method is nice because dropping the snapshot partition does not require any data copying. 2) are there any people using LVM for database snapshots? The Whitepaper from SuSE has examples for Oracle and the HOWTO's talk about it, but is it used in production? If so, what issues have you found? 3) what is the overall stability of snapshot functions? I have been following the pvmove thread with some alarm as I thought that LVM functionality was stable at this point. Is there a place that I can see what functionality is considered stable and what isn't? The mailing list archives do not paint a rosy picture of snapshot functionality. 4) It seems that most of the LVM work is going into 2.4. We have not been particularly pleased with the stability of 2.4 in general and would like to stay with 2.2 for a while. How does the stability of LVM on 2.2 compare to 2.4? 5) I have seen references to the VFS lock patch in the mailing list. Is this actually supported by any filesystems yet? Is it in the kernel proper? Thanks. Best, Kyle -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - MicroTelco Services saves money on every Fax: - Fax to email (FREE) - Fax to PSTN based Fax (Up to 95% Savings) - Fax Broadcasting: Send 100s of faxes to fax machines and email addresses in the time it takes to send just one! =========================================================== So send a fax today and let us know what you think! For more info. visit: www.internetfaxjack.com ===========================================================