On Tue, Feb 14, 2012 at 3:02 AM, <keld@xxxxxxxxxx> wrote: > On Tue, Feb 14, 2012 at 01:40:25AM +0400, CoolCold wrote: >> On Mon, Feb 13, 2012 at 4:09 PM, Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx> wrote: >> > On 2/12/2012 2:16 PM, CoolCold wrote: >> >> First of all, Stan, thanks for such detailed answer, I greatly appreciate this! >> > >> > You're welcome. ?You may or may not appreciate this reply. ?It got >> > really long. ?I tried to better explain the XFS+md linear array setup. >> > >> >> There are several reasons for this - 1) I've made decision to use LMV >> >> for all "data" volumes (those are except /, /boot, /home , etc) ?2) >> >> there will be mysql database which will need backups with snapshots 3) >> > >> > So you need LVM for snaps, got it. > > > Well, I do not think LVM gives you snaps. I think you need to close down the mysql database > to have a consistent DB, then make backup, then reactivate mysql. I may be wrong, tho. You are a bit wrong here. MySQL in general supports two storage types - MyISAM & InnoDB. While InnoDB is ACID transactional engine, MyISAM isn't. So, one should be able to backup InnoDB with snapshots without interrupting workload and it will do recovery/transaction rollbackup on startup. For MyISAM engine, snapshots will produce unpredictable results as partial update may happen. But, snapshots are useful in any case, because they allow to do backup in 4 steps: 1) "FLUSH TABLES WITH READ LOCK" - this will flush all buffers and close databases 2) lvcreate -s && unlock tables.... - doing snapshot of data and releasing lock 3) copying it somewhere 4) lvremove .... - releasing snapshot So, in such situation, work will stop for 1) & 2) , not cosuming time for 3) . > LVM is great if you want to resize partitions. XFS cannot be shrinked, tho, only grown. > For snapshots you need somthing like btrfs. But to have the DB consistent you need to close it > before taking a backup. > > And anyway, I think a 7 spindle raid10,f2 would be much faster than > a md linear array setup, both for small files and for largish > sequential files. But try it out and report to us what you find. Quick & dirty iozone doesn't show this yet ... > > I would expect a linear md, and also most other MD raids would tend to perform better in > the almost empty state, as the files will be placed on the faster parts of the spindles. > raid10,f2 would have a more uniform performance as it gets filled, because read access to > files would still be to the faster parts of the spindles. > > > best regards > Keld > > --- [snip] -- Best regards, [COOLCOLD-RIPN] -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
