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SAN Storage for Backup iSCSI vs Direct Attached

Posted on 2015-01-15
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Last Modified: 2016-02-25
We use a physical server running VEEAM Backup and Replication to backup our virtual environment.  Our VEEAM backup server connects to iSCSI storage over 1GB links and has a direct attached SAS backup drive.  I notice in the mornings when we copy our backup files to tape, the 1GB iSCSI link is always 100% utilized.  I got to wondering if we'd be better off with direct attached storage for this setup.  How much faster would it be going from direct attached storage to direct attached tape vs going from iSCSI storage to direct attached tape?  The tape device is an HP LTO5.

If using direct attached SAS storage is the way to go, what is a lower end SAN that would work well and could provide about 10TB of space?
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Question by:jpletcher1
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13 Comments
 
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Expert Comment

by:sr75
ID: 40551778
Part of the speed is the number of disks in the array.  It is faster to write to ten 7500 RPM SCSI drives then to one 15000 RPM SAS drive.  

I am assuming you have an iSCSI disk array and maybe a local raid 5 of 3 SAS drives.  Do you know the speeds of the drives in question?

If they are comparable (say both are 10k RPM) then I would most definitely look at revamping the iSCSI network to improve the available bandwidth.
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Author Comment

by:jpletcher1
ID: 40551836
There are 16 10K disks in the iSCSI array.  The limitation seems to be on the 1GB  iSCSI network connection, which is why I am asking about direct attached storage for this.
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Expert Comment

by:andyalder
ID: 40552200
Copy to tape is fairly sequential although de-dupe makes it a bit random, therefore high capacity 7.2K disks are fine, sequential access is good due to the high areal density. LTO5 runs at 140MB/s native and assuming compression you may push that to 250MB/s, fortunately data rate matching means the tape can slow down to 47MB/s so at least it won't be shoe-shining.

What is the current iSCSI SAN you have, there may be a SAS host connect card for it to give 12 or 24 Gb/s, that would be far cheaper than a whole new unit.
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Author Comment

by:jpletcher1
ID: 40552401
We have a HP MSA G3 P2000 SAN.  I don't believe you can change it from iSCSI to DAS, but I could be wrong.
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Expert Comment

by:andyalder
ID: 40552587
With luck you might be wrong.

For the Large Form Factor chassis there are both intelligent RAID controllers with host-based SAN attachment and dumb SAS interface cards that plug into the same chassis, For the 24 disk 2U version there isn't a dumb interface module.

Go to http://www8.hp.com/uk/en/products/disk-storage/product-detail.html?oid=4118559 and click on quickspecs link.

Don't think the dumb JBOD interface cards are certified to attach to Smart Array controllers though and the intelligent SAS host attach version costs as much as the FC or iSCSI variant.
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Author Comment

by:jpletcher1
ID: 40554118
I guess my first question is with the option of the data being written to tape, what is the difference between a 1GB iSCSI connection to storage vs DAS?  Is the 1GB iSCSI link a huge bottleneck with a tape drive and how fast it can write data?  

My understanding is at maximum, a 1GB iSCSI connection could transfer data at 125mb/sec and our tape drive can write at 140mb/sec or 280mb/sec with compression.  Given that, and DAS would be able to transfer to tape much faster correct?
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Expert Comment

by:andyalder
ID: 40554159
SAS attached would be faster but does it matter how long it takes to copy from the backup-to-disk unit to the tape drive?
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Author Comment

by:jpletcher1
ID: 40554267
Yes, on our full backup days the data being written to tape takes 8 hours and goes past the time our off-site store location is open that day.
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LVL 56

Expert Comment

by:andyalder
ID: 40554283
12 disk model only: Probably worth swapping the iSCSI controllers for SAS host interface ones then, HP P2000 G3 SAS MSA Array System Controller AW592B, you'll need a non-RAID SAS controller too to put in the server.
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Author Comment

by:jpletcher1
ID: 40554412
We have the 24 disk model, so you're saying this wouldn't be possible for us then right?
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Accepted Solution

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andyalder earned 500 total points
ID: 40554441
My bad, AW592B is supported in the 24 disk unit as well as the 12 disk one.
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Author Comment

by:jpletcher1
ID: 40558692
Thanks, I will check into either changing out controllers as well as maybe trading in our current MSA SAN for a SAS one.

I will mark your solution as the answer.  One side question if you don't mind giving your thoughts.   When we first got the MSA SAN it had 12 disks in it and I set it up with RAID6.  As I've now added 4 more disks to it, it seems to have gotten much slower as far as I/O.  I know 16 disks is the limit for the MSA RAID array.  Can an array actually perform worse after it reaches a number of disks or should it always get faster since there are more spindles involved?
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LVL 56

Expert Comment

by:andyalder
ID: 40559249
Added more disks to the same Vdisk? If so maybe it's still expanding in background, it certainly shouldn't get slower with more spindles.
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