[Veritas-bu] Fast backup to tape but slow backup to disk on NBU 5.1MP3

2005-08-15 22:22:55
Subject: [Veritas-bu] Fast backup to tape but slow backup to disk on NBU 5.1MP3
From: rob AT worman DOT org (Rob Worman (home))
Date: Mon, 15 Aug 2005 21:22:55 -0500
What a fascinating thread - thanks for the interesting test results, 

As for "what the netbackup fallout might be on a dssu loss", here's my 
crack at it:

Losing a disk storage unit is equivalent to a destroyed tape, just on a 
much larger scale :-(

Depending on your configuration and the state of the disk storage unit 
at the time of the loss, there are two potential scenarios that you'll 
be in:

For a given image...
(1)the lost disk storage unit had the only copy of the image
(2)the lost disk storage unit had the original copy of the image, but 
there are additional copies that also exist.

The immediate symptom of either of these scenarios would look 
similar... you would be able to browse these images for a restore, but 
once the restore is launched you're going to see lots of errors.  
(probably status code 174 or 85 failures)

The immediate resolution of either of these would also be similar - 
expire the invalid copy of the data from the catalog with bpexpdate 
-backupid -copy.

The difference between (1) and (2) lies in the end result of that 
bpexpdate.  You'll either lose the entire image because you had to 
bpexpdate your only copy from the catalog, or else your secondary copy 
will automatically ascend to primary and your restore attempts will 
work again.


On Aug 11, 2005, at 6:25 PM, Tim Berger wrote:

> Matt, writing multiple concurrent streams to the same set of disks may
> be hurting performance.  One at a time may yield better results.
> I'm in the process of building out some staging servers myself for nbu
> 5.1 - been doing a bunch of bonnie++ benchmarks with various configs
> for Linux using a sata 3ware controller.
> On fedora core 3 (I know it's not supported):
> Raid5, 5 disks I got ~30MB/sec writes & 187MB/sec reads.  Raid 50 with
> striping over 3 4-disk raid5's got 49MB/sec writes, 120 MB/sec reads.
> For raid0, w/10 disks, got a nice 158 MB/sec writes, and 190MB/sec
> reads.
> I'm partial to raid5 for high availability even with poor write
> performance..  I need to stream to lto3, which tops out at 180 MB/sec.
> If I went with raid0 and lost a disk, then a media server would take a
> dive, backups would fail, and I'd have to figure out what data failed
> to make it off to tape.  I'm not sure how I'd reconcile a lost dssu
> with netbackup.  If I wanted to to use the dssu's for doing synthetic
> fulls, then that further complicates things if a staging unit is lost.
> Any thoughts on what the netbackup fallout might be on a dssu loss?
> Even though it's not supported yet, I was thinking of trying out
> redhat enterprise linux 4, but I'm seeing really horrible disk
> performance (eg. 100MB/sec reads for raid5 vs the 187MB/sec on fc3).
> Maybe I should try out the supported rhel3 distribution. ;-)  I
> don't have high hopes of that improving performance at the moment.
> On 8/10/05, Ed Wilts <ewilts AT ewilts DOT org> wrote:
>> On Wed, Aug 10, 2005 at 12:43:39PM -0400, Matt Clausen wrote:
>>> Yet when I do a backup to disk, I see decent performance
>>> on one stream (about 8,000KB/s or so) but the other streams will 
>>> drop to
>>> around 300-500KB/s.
>>> SIZE_DATA_BUFFERS = 262144
>>> and I see this performance on both the master server disk pool AND a
>>> media server disk pool. The master server is a VxVM concat volume 
>>> set of
>>> 3x73GB 10,000RPM disks and the media server is an external raid 5 
>>> volume
>>> of 16x250GB SATA disks.
>> I don't believe you're going to get good performance on a 16 member
>> RAID5 set of SATA disk.  You should get better with a pair of 8 member
>> raid sets, but SATA is not fast disk and large raid 5 sets kill you on
>> write performance.  If you're stuck with the SATA drives, configure 
>> them
>> as 3 4+1 RAID5 sets and use the 16th member as a hot spare.  You'll 
>> have
>> 3TB of disk staging instead of about 3.8TB but it will perform a lot
>> better.
>> --
>> Ed Wilts, Mounds View, MN, USA
>> mailto:ewilts AT ewilts DOT org
>> _______________________________________________
>> Veritas-bu maillist  -  Veritas-bu AT mailman.eng.auburn DOT edu
> -- 
> -Tim
> _______________________________________________
> Veritas-bu maillist  -  Veritas-bu AT mailman.eng.auburn DOT edu