I think to make an informed decision you would need to look at the
bigger picture. Your original goal was to increase your backup
performance and shrink you backup window
Disk can be great but don't expect your backup times to increase just
because you are using it.
Is your disk being provided from the same array where your backup
clients host their data? In that case you could see a reduction in
performance.
Also you could have a negative effect on your production systems when
de-staging during the day
What kind of Networking do you have in place between your backup clients
and your media servers?
Using GbE with Jumbo frames can produce some fantastic results in
shrinking you backup window.
What kind of tape devices do you have and how many?
In most cases you will have equal tape throughput capability to that of
your disk or very likely even more.
Of course you don't want to multiplex too high but with efficient
networking you may not need to. - you should also make sure you perform
all the NetBackup tuning you can e.g. number/size data buffers and
network buffers on media servers and clients whether using disk or tape
I like to use disk for slow backup clients that would force a high level
multiplexing setting or cause shoe shinning across your tape devices.
Where you have servers (i.e. DB systems or systems with large files)
that have the potential to stream at a decent rate - send them direct to
tape.
-----Original Message-----
From: veritas-bu-bounces AT mailman.eng.auburn DOT edu
[mailto:veritas-bu-bounces AT mailman.eng.auburn DOT edu] On Behalf Of Travis
Kelley
Sent: 06 May 2010 11:57
To: Martin, Jonathan; Victor Engle; veritas-bu AT mailman.eng.auburn DOT edu
Subject: Re: [Veritas-bu] Architectural question (staging)
I agree with Martin here on them "working" in some cases. I have and
EMC Clariion with 45 1TB SATA disks and I can tell you it screams. I
routienly see over 600MB/S out of the array wjile destaging. Sure, I
have a larger and potentially "smarter" array than some but to say
they don't ever work is wrong.
One other point in regard to fragmentation. If you are truely using
the disks as a cache and aren't in need of the additional restore
performance they provide then as soon as destaging is done you can
just expire all of the images on disk. Once you have them on tape,
you may not "need" them on disk anymore anyway. If you are able to do
this somewhat regularly (as often as you determine is necessay to keep
performance up), fragmentation becomes a non-issue. In my case
fragmentation has never been an issue anyway, because of the extremely
wide striping. But if its an issue, as long as you can clean down
the disk every once in a while, the problem goes away.
Also images are interleved on the disk in the sense that they are not
contigious on the disk from a block perspective, but the image files
are not "multiplexed" as they would be on tape. Every backup image
has at least one file all its own.
Hope that help.
Travis
On 5/5/10, Martin, Jonathan <JMARTI05 AT intersil DOT com> wrote:
> I'd hate not to disagree with someone as grumpy and disagreeable as
Ed.
> Personally, I wouldn't take advice on this matter from someone who
> "worked with disk staging units for at least a year" and "gave up."
> (Also, I think Ed is a wet blanket.) I had this thing figured out 4
> years ago when we first implemented DSSUs in production. I may not be
> the biggest NBU shop on the planet, but I back up more than 50TB a
week
> using this method exclusively, so I can tell you that it does work.
>
>
>
> As far "interleaving", there is most certainly interleaving at the
file
> system level when you run multiple streams to a DSSU. How Ed can say
> there is no interleaving and then tell you to watch your disk
> fragmentation is beyond me. Fragmentation = disk interleaving as far
as
> I am concerned. The point is that the files are non-contiguous.
>
>
>
> Here's my proof.
>
>
>
>
>
>
>
> This is a snippit of a utility called DiskView from SysInternals /
> Microsoft. The yellow bits are the actual 1K fragments of data on disk
> for that image file above. The little red dots indicate the beginning
> and end of file fragments. There are 64 little yellow dots between the
> red dots indicating my 64K clusters.
>
>
>
>
>
>
>
> Here's that same section of disk, different image file. These two
> streams ran simultaneously last night (along with 6 others) and I can
> guarantee you that the top image wrote faster, and will destage to
tape
> faster than the image below.
>
>
>
> Why? Imagine you are bpdupicate.exe requesting the first file back to
> write to tape. Compared to the 2nd image, you are going to get a lot
> more reading done and a lot less seeking as your head(s) cross the
disk
> to pickup fragments. Or, so goes my theory. There is a utility
> available from Dell that will show me the amount of time spent reading
/
> writing versus seeking per disk but I didn't have the time to acquire
it
> and test.
>
>
>
> Now, I know there are variables here. As I stated before, one of the
big
> improvements to my speed was using a 64K cluster size. Last time I
> checked this wasn't available in Unix/Linux. Then again, ext2/3 file
> systems also like to leave "space" between their writes to account for
> file growth, which may help (but I doubt it.) I intended to test this
> several years back, but my management put the kibosh on Linux media
> servers. The raid controller, simultaneous read/write, spindle count,
> and disk type also add a lot of variability.
>
>
>
> I haven't tested any of this on a SAN volume, only on direct attached.
I
> don't think there is much to be gained by taking a 6TB lun and
> partitioning it at the OS or breaking it into multiple luns at the
SAN.
> After partitioning, the entire DSSU is still on the same raid group /
> set, which ultimately controls your performance. If you could take
your
> 6TB lun and break it into 3 x 2TB raid groups / luns then I think that
> would help. I've actually considered breaking my 14 disk RAID5s into
14
> single disks for performance testing (single stream each), but that's
an
> entirely different management nightmare (14 DSSUs per media server
> etc...) A single SATA disk can drive LTO3, assuming the data is all
> nicely lined up. The minute that head has to go seeking, you are in a
> world of hurt.
>
>
>
> Again, I would start with a single stream to that 6TB DSSU and see
what
> you get both writing to the DSSU and destaging to tape. Whatever
> performance you get out of that configuration is your best case
> scenario. Multiple streams or creating multiple partitions will only
> drag your numbers down. The crux of the issue (at least for me) is
> balancing the number of streams I need to run to get my backups to
DSSU
> within my windows, versus the destaging speed I need to get that data
> off to tape on time.
>
>
>
> Good luck,
>
>
>
> -Jonathan
>
>
>
>
>
> From: veritas-bu-bounces AT mailman.eng.auburn DOT edu
> [mailto:veritas-bu-bounces AT mailman.eng.auburn DOT edu] On Behalf Of Ed
Wilts
> Sent: Wednesday, May 05, 2010 4:06 PM
> To: Victor Engle
> Cc: veritas-bu AT mailman.eng.auburn DOT edu
> Subject: Re: [Veritas-bu] Architectural question (staging)
>
>
>
> On Wed, May 5, 2010 at 2:57 PM, Victor Engle <victor.engle AT gmail DOT com>
> wrote:
>
> So my question is how best to configure the DSSUs with the goal of
> optimized de-staging. I will have 6TB to configure as desired on the
> backup server. If I understand correctly, the more concurrent streams
> allowed to the DSSUs, the slower the de-staging because of interleaved
> backup streams.
>
>
> The DSSU consists of a set of files with each file being a backup
image
> and you define the maximum size of each file within an image. There
is
> no "interleaving". When you destage, one image at a time goes to
tape.
>
> Watch your fragment sizes and watch your disk file system
> fragmentation...
>
> .../Ed
>
>
>
> Ed Wilts, RHCE, BCFP, BCSD, SCSP, SCSE
> ewilts AT ewilts DOT org
>
> Linkedin <http://www.linkedin.com/in/ewilts>
>
>
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