Hardware Update to Overcome I/O Contention

BDMcGrew

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PREDATAR Control23

((( If I'm in the wrong forum, mods, please feel free to move the thread. I didn't see a better place to put this one )))

Good morning, I'm currently running TSM 7.1 in CentOS 6.7 on one half of a Supermicro SuperServer 6016TT. It's a Dual Xeon box with 24GB of RAM, a 4gb FC card, booting from a 32GB SSD and using a 4TB SSHD for TSM diskpool with a 2x48 LTO4 4GB/FC library behind it directly connected to the FC card.

It all works fine but I'm having serious contention getting data out the tapes fast enough. No surprise there, that 4TB SSHD is not the fastest drive in the world. I'm not necessarily looking to grow the disk pool, just resolve the contention issues.

I'm wanting to know if I would be better off replacing the 4TB SSHD with a 1TB SSD directly. Or, if I should be looking at a FC switch and FC SAN with an array of disks to use for my diskpool. Which is going to do a better job at overcoming this problem?

Thanks,

-brian
 
PREDATAR Control23

I am surprised (if I read it correctly) that you are using a single 4 TB SSHD. The size and geometry of the drive will definitely be slow. However, this may not be totally the issue.

I did not get any info (again, if I read your post correctly) on the number of tape drives in the library. The basic rule I follow is to have 2 tape drives maximum per 8 GB fiber. A 4 GB fiber can be used as long as you don't see the FC getting saturated. For the 4 GB FC card, this means that you can only pump out a maximum of 2 GB (giga bits) per tape drive. This is the reason why I use 8 GB FC cards: to remove the possibility of contention.

Further, higher FC card speeds can sustain more traffic and allows for the use of more tape drives per single FC card. I use this in conjunction with a FC switch.

I suggest this to improve transfer speed:

- replace the disk storage pool with a RAID array using smaller disk drives
- limit single FC card connection to 2 tape drives. This means that if you have 8 tape drives, use 4 FC cards
- Install a FC switch between the TSM server and tape library so zoning can be introduced. This makes your setup flexible and possibly play with the number of FC cards needed by using higher speed FC cards. Of course, the FC switch should be able to handle higher FC speeds
 
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PREDATAR Control23

Most high capacity SSHD's use 5400rpm disks, so the highest sequential throughput with a single disk going to a single drives will be around 100MB/sec (with large files). With two migration sessions running from this disk then the throughput will be less than half of this due to the time required for the heads to move between the relevant sectors on the disk. file fragmentation and file size will also have a big impact on migration speed, this is where the number of iops the drive can perform are important. I doubt the NAND cache on the SSHD will be in use during migration, if it is then it will be write-through so that will not offer any increase in I/O and if poorly optimized for sequential reads it may even impact performance if it attempts to do any read ahead caching?

I echo what moon buddy has stated. If you want to improve throughput you will need more disks for the diskpool, if you do not have room in the server chasis for more disks then these will need to use separate HBA adapters from the tape drives, as you should never mix disk and tape traffic on the same HBA ports.
 
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