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owiking
Joined: 05 May 2009
Posts: 1
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 Posted: Wed May 06, 2009 1:10 am Post subject: Netbackup 6.5 DSSU fragmentation |
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Hi
Im having problems with my diskstage getting to fragmented and thus getting very slow performance when duplicating to tape. Running defrag isnt an option since the files are reaplced fequently and the defrag job will take to long time to run.
From what Ive seen and read, this is a major problem for alot os users of Netbackup.
Is there a way to force Netbackup to preallocate space on the diskstage for each backupjob, instead as it is now that they are all written in fragments all over the disk?
Ive read some about the differences with Basic and Advanced diskstages in Netbackup, Im running Basic atm, but havent found any information that Advanced could preallocate space?
My diskstage is 5.5tb large, is it better to make to divide it to 2-3 partitions to avoid fragmentation?
thanks |
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cpreston
Site Admin
Joined: 04 May 2007
Posts: 783
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| Posted: Wed May 06, 2009 8:16 am Post subject: Re: Netbackup 6.5 DSSU fragmentation |
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| owiking wrote: | | Im having problems with my diskstage getting to fragmented and thus getting very slow performance when duplicating to tape. Running defrag isnt an option since the files are reaplced fequently and the defrag job will take to long time to run. From what Ive seen and read, this is a major problem for alot os users of Netbackup.thanks |
This IS a common problem that people have, and is one of the reasons that some people prefer VTLs. VTLs have a specialized file/storage system that is designed to handle the types of I/O that backups create. Regular filesystems are designed to support random I/O, where backups are very sequential I/O.
The only thing you can do to minimize fragmentation in your setup is to completely fill and completely empty the system every night. When the diskstaging cache is completely emptied, then backups written from that point on will not be fragmented.
However, if you are going to completely empty your cache, do so just before your backup so that last night's backup is around as long as possible for restores. |
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ewilts
Joined: 13 Jul 2007
Posts: 600
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| Posted: Wed May 06, 2009 8:38 am Post subject: Netbackup 6.5 DSSU fragmentation |
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It's not just a fragmentation issue - a defrag'ed file system may also give you poor destage performance.
A bunch of people have reported this issue but so far nobody has found the smoking gun. It's an issue on multiple platforms as well.
.../Ed
On Wed, May 6, 2009 at 4:10 AM, owiking <netbackup-forum < at > backupcentral.com ([email]netbackup-forum < at > backupcentral.com[/email])> wrote:
| Quote: |
Im having problems with my diskstage getting to fragmented and thus getting very slow performance when duplicating to tape. Running defrag isnt an option since the files are reaplced fequently and the defrag job will take to long time to run.
From what Ive seen and read, this is a major problem for alot os users of Netbackup.
Is there a way to force Netbackup to preallocate space on the diskstage for each backupjob, instead as it is now that they are all written in fragments all over the disk?
Ive read some about the differences with Basic and Advanced diskstages in Netbackup, Im running Basic atm, but havent found any information that Advanced could preallocate space?
My diskstage is 5.5tb large, is it better to make to divide it to 2-3 partitions to avoid fragmentation?
.../Ed
Ed Wilts, RHCE, BCFP, BCSD, SCSP, SCSE
ewilts < at > ewilts.org ([email]ewilts < at > ewilts.org[/email]) |
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amellor.au
Joined: 17 May 2007
Posts: 21
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| Posted: Wed May 06, 2009 11:36 pm Post subject: Netbackup 6.5 DSSU fragmentation |
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I have come across issues with our disk staging units as well, but it is not fragmentation...
out of two media servers, only one presents the symptom of de-staging slowing down.
System A - Master Server, Solaris 10 Sparc, 2x DSU's (each 4x 4+1 FC attached SATA disks) formatted VXVM/VXFS.
System B - Media Server to System A, Solaris 10 Sparc, 1x DSU (4x 4+1 FC attached SATA disks) formatted ZFS.
System B gives us consistent performance, month in month out.
System A works great, better than System A (by about 50MB/s). However, there is a noticeable decrease in de-staging performance (probably staging performance as well, but who is up at 11pm to see that) after about 2 weeks of system uptime. and after about 4 weeks the issue is blatantly staring us in the face, we see about only 50MB/s of de-staging performance.
The last time this issue hit us I did some tests, dd from DSU to tape = Slow, dd from DSU to null = Slow, dd from zero to DSU = Slow, DD from Zero to tape = FAST  . ok, I'm happy it is not tape subsystem, I thought for a moment I have a ZFS mirror of 2x 2.5" SAS disks on System A, copied a Large image from DSU to the SAS disk. I performed first the dd test of that image to null from the DSU, still slow. OK, I performed the dd test from SAS to null = Fast. Wait, What a single 2.5 SAS disk is faster that 16x SATA disks ? No way.
I knew through previous experiences that a reboot clears (temporarily) the symptom. and on this most recent experience I rebooted, and as soon as it returned, dd from the DSU to null = Blazingly Fast.
I will be replacing the VXFS DSU's with ZFS in the future.
Regards
Adam.
From: veritas-bu-bounces < at > mailman.eng.auburn.edu [mailto:veritas-bu-bounces < at > mailman.eng.auburn.edu] On Behalf Of Ed Wilts
Sent: Thursday, 7 May 2009 12:38 AM
To: VERITAS-BU < at > mailman.eng.auburn.edu
Subject: Re: [Veritas-bu] Netbackup 6.5 DSSU fragmentation
It's not just a fragmentation issue - a defrag'ed file system may also give you poor destage performance.
A bunch of people have reported this issue but so far nobody has found the smoking gun. It's an issue on multiple platforms as well.
.../Ed
On Wed, May 6, 2009 at 4:10 AM, owiking <netbackup-forum < at > backupcentral.com ([email]netbackup-forum < at > backupcentral.com[/email])> wrote:
| Quote: |
Im having problems with my diskstage getting to fragmented and thus getting very slow performance when duplicating to tape. Running defrag isnt an option since the files are reaplced fequently and the defrag job will take to long time to run.
From what Ive seen and read, this is a major problem for alot os users of Netbackup.
Is there a way to force Netbackup to preallocate space on the diskstage for each backupjob, instead as it is now that they are all written in fragments all over the disk?
Ive read some about the differences with Basic and Advanced diskstages in Netbackup, Im running Basic atm, but havent found any information that Advanced could preallocate space?
My diskstage is 5.5tb large, is it better to make to divide it to 2-3 partitions to avoid fragmentation?
.../Ed
Ed Wilts, RHCE, BCFP, BCSD, SCSP, SCSE
ewilts < at > ewilts.org ([email]ewilts < at > ewilts.org[/email])
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