From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kyle Hayes Subject: Re: [linux-lvm] snapshot questions References: In-Reply-To: MIME-Version: 1.0 Message-Id: <0111021505181G.08803@khayes-lin> Content-Transfer-Encoding: 8bit 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 17:04:02 2001 List-Id: Content-Type: text/plain; charset="us-ascii" To: linux-lvm@sistina.com, Kenny Gorman On Friday 02 November 2001 13:59, Kenny Gorman wrote: > I will try to quicky summarize what _I_ do: > > - Yes snapshots work. > - No, it's not a 1 to 1 disk usage ratio between the vg and the snapshot > vol. It's much less. I dont know how to test for fullness using > Linux/LVM yet. > - I use Oracle, your DB may be different. > 1) put the tablespaces in hot backup mode > 2) take a snapshot (mount the snapshot vol) of the volume/s that the > tablespace is on > 3) take the db out of hot backup mode. I use MySQL in a mode that uses files in the filesystem. Does your Oracle installation use raw disk or files? If it is raw disk, then I probably need to do something that will flush disk changes somehow. I am hoping that the VFS hooks will make the filesystem flush its buffers to disk so that I don't get a snapshot full of garbage. I suppose that Oracle will flush all buffers to disk (thus making a coherent disk image) when you put it into hot backup mode. When I tell MySQL to flush its tables, it simply writes out everything it can, closes and reopens the files. Thus it is up to the filesystem/OS to get the data to the disk in a reasonable fashion. Interestingly, this may imply (and this seems to be in line with some of the responses I read) that journaling filesystems may actually be more of a problem than non-journaling ones. Weird, but seems to make sense. > - I also do some checkpointing, etc in my script. We keep live remote replicas, but sometimes the replica needs to be rebuild. In that case, it is very important to have a means of getting a completely coherent database snapshot. Right now, this process is very carefully done with lots of highly database specific code. Ick. It is a pain to maintain and has a lot of edge cases that we find from time to time :-) We'd like something a little simpler and more complete. > - the tape drive can then get the backup from the snapshot. In our case, we spool it off remotely, but I get the idea. > - You would restore the image from tape, to a new or the orig. volume > when you recover. > - no noticable effect on end users, it's a 24/7 thing. Restores work > fine. So you have this in production? > It's really not all that scary. Sorry for not going into more technical > detail. No problem. I am still figuring out how to deal with LVM. It looks like the solution to all our problems, but I want to make sure before we spend more time on it. Our existing solution works, but it costly to maintain. 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 ===========================================================