RP5740 with DS2100s, move to DS2405 fiber channel?

[Peter Moore_1]

Attached to our rp5470, we currently have 2 DS2100's loaded with total of 8 x 18.2GB 15k Drives. (4 mirrored). Application performance is slow (disk access is bottleneck) and disk space running out. I'm considering replacing these units with DS2405 and 14 x 18.2GB 15K FC drives. This will give me some more disk space and (i'm hoping) increase my throughput when accessing data on disk. Is my logic correct? Will I see a performance improvement by switching from SCSI (ultra2) ds2100 to the Fiber Channel scenario on ds2405? Any issue with compatibility with rp5470 running HP-UX ver 11.0 ??
Any thoughts, comments would be appreciated!!

[Jeff Schussele]

Hi Peter,

Absolutely you should see a perf increase.
FC blows away copper SCSI every time.
You might also want to investigate whether the DS2405 would support the newer 2GB XL2 fibre channel cards or only the older style 1GB 5158 FC cards. But either way you're going to see easily measurable perf gains.
Also NOW is a good time to see whether laying out the disks differently (striped?, stripe size, RAID type, etc.) might be beneficial as well.
As to compatibility, I don't see any obvious problems, but running 11.0 & not 11i I would make sure you're entirely up-to-date on patches including LVM, FC & VXFS.

Rgds,
Jeff

[Joshua Scott]

If you have your 2 DS2100s on separate HBA's then your throughput should be a full 80 MB/s. since you have a total of 4 data disks that each HBA is writing to, you have a throughput per disk of 20 MB/s if you are maxing out the SCSI bus.

Using a 2Gb FC card to connect to the DS2405, you get 200 MB/s for the enclosure, but you are using just 1 FC card to write to all 14 disks. this gives you only a little more than 14.25 MB/s per disk. even if you set up the DS2405 with 2 controllers, and used 2 HBAs, you would still only acheive 28.5 MB/s writing speed per disk.

The Reading speed on the DS2405 would be 28.5MB/s per disk no matter what setup you use.

Since you say that you have Ultra2, I would suggest replacing the Ultra2 cards with Ultra160 cards. 2 U160 cards would acheive 40MB/s per disk.

Once you factor in the cost, replacing the HBAs will only cost you about $2,500; whereas the new disk enclosure, new disks, new FC cards would be around $15,000.

Remember that Fibre is not much faster than SCSI. Actual transfer rates on currently used Interface cards:

SCSI:
Ultra2: 80MB/s
Ultra160: 160MB/s
Ultra320: 320MB/s

Fibre:
1Gb: 100 MB/s
2Gb: 200 MB/s

Hope this helps!

-Josh

[Leif Halvarsson_2]

Hi,
Maybe you will get better performance but perhaps not due to the FC but more to the larger number of disks. In most cases where you have disk bottlenecks the problem is not the transfer rate , it is the disk io (IOPS). Increasing from 8 to 14 disks will perhaps give better performance, it depends how the disks is used (is all disks equal loaded).

I would suggest you to consider a hardware RAID controller. A FC is of course a good (but expensive) solution. An alternative is the RAID 160 controller:
http://www.hp.com/products1/unixserverconnectivity/storagesnf2/raid160/index.html

With four SCSI 160 channels for disk storage you can connect one DS2100 to each channel. With 16 15k disks and the RAID controller offloading the cpu from disk handling I am sure you get better performance then with 14 disks and software mirroring. The RAID controller also makes it possible to get optimal utlization of every disk.

[Leif Halvarsson_2]

Hi (again),
I had a look at the specifications for the RAID 160 and it seems as only the 4300 JBOD is supported. I am not sure why (I doubt it should be any tecnical problem). Of course it is nothing wrong with the 4300 but one idea with my solution was to keep your current DS2100 (as the disks is fast 15k) and complete with 2 DS2100 to get 16 disks.

But, if there is any problem with the RAID 160 you can use the RAID 4Si instead, it support DS2100.

http://www.hp.com/products1/unixserverconnectivity/storagesnf2/adapter14/index.html

[Joshua Scott]

Leif,

The Raid Cards you are referencing use RAID5, which I'm sure wouldn't help his access time, Especially if his App is write intensive. The Software mirroring has nearly no overhead, and if the DS2100s are on separate channels, then there shouldn't be much of a performance difference between those and a nice fibre JBOD.

[Leif Halvarsson_2]

Hi,
Both cards support several RAID levels and at least RAID 1+0 (striping/mirroring) and RAID 5 (parity). It is possible to configure multiple RAID sets, for example one RAID 1+0 (for write performance) and one RAID 5 (better disk space utilization). There is also a number of other features with a hardware RAID (e.g hot spare disk).

Using a FC JBOD in a point to point connection will make very little advantage compared to a SCSI JBOD (but to a higher cost). The main idea with FC is not speed, it is connectivity (if you want to connect several hosts to a storage system).

I am still convinced about you will get more performance and flexibility for your money with a hardware SCSI RAID solution then with a FC JBOD.

[Peter Moore_1]

Thank you all very much for your feedback and recommendations. A few things have come to mind thus far based on your comments:

My primary objective is to increase disk access/response time... Since I'm now needing to add more disk space, I'm trying to choose the most sensible "next step" (option 1) add 2 more DS2100's and load them up with drives in a mirrored configuration (HP MIRRORDISK/UX) 8 disks mirrored onto 8 other disks... or (option 2) switch to FC10 or DS2405 and replace all the disks entirely...

Current config:
rp5470 with 2 internal 36gb drives for O/S stuff.
2 x DS2100s fully populated (4 drives in each, software mirrored, giving me 4x18.2GB 15K useable space), only 1 scsi cable on the back of each DS2100 going to 2 single port ultra2 scsi hba a5149A cards.

Looks like the 4 drives in the first DS2100'
s are all sharing one a5149a PCI ultra2 scsi interface.

since i want speed of access and lots of disks (my application likes lots of disks, so i can spread the database tables across different physical disks for simultaneous access), maybe i should just add 2 more DS2100,... get 8 more drives... (maybe even upgrade to ultra3??) but add *6* ultra2 scsi channel cards?? or 3 with dual channel cards???? i think i need to increase the number of ways the data can reach the bus. some folks have mentioned that getting a FC10 or 2405 with loads of disks.., you still have to share the single pipe with all the disks, so it may actually slow things down !! hmmm...........

Again, thanks for all your assistance. It helps to talk it through...........

[Bernhard Mueller]

Peter,

basically Joshua and especially Leif are absolutely correct:

- if you need disk performance you need striping.

- for safety you need mirroring.

- without a RAID system, LVM lets you only use distributed extents, which in turn has drawbacks and limitations (min. 1MB PE size, which is typically too large, the max extents per VG limitation would require to use even 2MB extents to be able to distibute across 2 times 3 disks in separate PVGs, etc.)

- so you need RAID.

Therefore, in your case I'd bet a VA7400 would be too expensive. Which leaves you with the RAID 4Si card.

With that card(s) you can contniue to use your existing HW *and* get a considerable boost in throughput using a reasonable stripe size *and* cache *and* have a simple LVM setup.

As Joshua said, just switching to an FC JBOD will not necessarily get you a big gain.

However, note that you will have to backup and restore your data.

Regards,
Bernhard

[Peter Moore_1]

Thank you Bernhard,

So it sounds like RAID is the way to go.. this would mean that I would no longer use the Single port ultra2 scici a5149a's..., but get 2 more DS2100s.. load 'em up with Ultra160 drives (18.2gb 15k) plug all 4 resulting ds2100's into the 4 ports of the Raid 4Si (a5856a), reconfigure.., load from backup... (glad my O/S is on internal drives..., backup/restore will be MUCH easier...)

What's the raid160 sa scsi a7143a, compared to the RAID 4Si...? Anyone know?? Do I want one over the other?