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Why is the PowerVault 725N server backing up so slowly?

Posted on 2011-05-11
Medium Priority
Last Modified: 2012-05-11
I use a PowerVault 725N ( Rackmount NAS Appliance) as a file server getting backed up via Symanctec. The current backup rate is at 299 MB/Min. I understand that since its a file server it will have many directories that decrease the backup rate but should it decrease it that much?

Everything is on Gigabit switches.

I tested the read write rate to the NAS  its seems very slow.
Sequential Write  239MB in 65.67s = 3.6MB per second = 216 MB/Min
Sequential Read 239MB in 33.00s = 7.2MB per second = 432 MB/Min

Is there anything that I can do to increase the backup rate?
Question by:fstinc
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LVL 47

Expert Comment

ID: 35742081
Enable the write cache on the RAID controller.
LVL 47

Expert Comment

ID: 35742175
Getting under 10MB/sec with that RAID controller in RAID5 mode and using those IDE disks isn't that unusual, BTW.  If you redo the RAID configuration to use the smallest block size possible then you might at best get to 20MB/sec, but then other types of workloads would actually get worse.

Here is a 3rd party benchmark that confirms performance ... you're pretty much getting all you are going to get


Author Comment

ID: 35742256
Thats kind of the same setup we have. Raid 5 as well as IDE disk. Actually I should confirm the IDE disk but nonetheless its similar. Do you think that Enabling write cache will help a decent amount? To be honest, I wouldnt know where to enable. Can you point me in the right direction to get this information?

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LVL 47

Accepted Solution

David earned 2000 total points
ID: 35742427
You can enable the write cache by going to the BIOS after rebooting it.  Can't remember where it is, but think it is a setting made on each of the LUNs,  look for setting write-back cache, which is enabling the cache.

Setting write-through cache disables the cache (i.e, each i/o writes through the disks, and you don't get a return code until operation is done).

Note, it will help, but don't do this unless you have a UPS, and personally I wouldn't do this if those disks were more than a few years old.  You can't upgrade the storage unless you are willing to add an external PCI SAS/SATA RAID controller, and an external disk subsystem unless you want to just blow off proper FCC, grounding, and get out some duct tape, if you crack them open you will see you are really limited on what you can do internally.

They are great, reliable machines, but they have no significant I/O capability unless you go to external storage.   Personally, I would retire them as soon as you can.
LVL 47

Expert Comment

ID: 35742440
No, they have IDE disks , I have 4 725Ns. (Had them, until they were retired).

Author Closing Comment

ID: 35748761
Thanks. Tons of help

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