Creating a 3TB RAID array; how does multilane SATA work?

[mherdeg]

Hi,
My real question is a technical one, about what eSATA means and whether multilane support means I'll see 12 drives using a host with 3 multilane ports and an external array with 12 drives.

I'd like to use software RAID-5 to make a storage server, of array size about 3 terabytes. Budget is $3000; rackmountable device strongly preferred as we have limited space and an existing rack.

We have lots of existing hardware that could help do the job. In particular, one solution I had in mind was buying some drives ourselves, using an external enclosure like this one*, installing a PCI-X 3x eSATA multilane-compatible host controller in our spare Apple Xserve, and using OS X's built-in RAID 5 support to make a storage server volume.

* No Astroturfing intended; any other product would probably be fine too.

The above array bills itself as holding 12X SATA2 drives and outputting as 3x eSATA. I know this suggests performance degradation (data for 4 drives going across one cable); I don't really care about transfer speed, as the server's intended for "almost archival" use rather than day-to-day.

Will this work? In particular, does multilane SATA mean that OS X will properly see twelve distinct drives in the above array, and will be able to make a RAID-5 volume out of them? If not, what should I use? (Any other recommendations for achieving 3tb, with a rackmount form factor, at $3k?)

(edit: My link was broken.)

 

[RebateMonger]

n.m.

 

[ForumMaster]

you don't need 12 drives to have 3tb. just get 4 seagate 7200.10 750GB drives. you can put them in a mush cheaper enclosure with enough channels and OS X should see them all.

 

[mherdeg]

Originally posted by: ForumMaster
you don't need 12 drives to have 3tb. just get 4 seagate 7200.10 750GB drives. you can put them in a mush cheaper enclosure with enough channels and OS X should see them all.

For RAID, of course, I'd need 5x 750GB. The current price for those is, say, $1800. (And I'd really prefer to have one hot spare, too, so we can have a day or two turnaround to find a replacement drive -- which means a 6-drive controller, and a cost of say $2100.)

RAID-5 with a standby drive is substantially cheaper with cheaper-per-gigabyte drives, which is why I strongly prefer that option.

 

[ForumMaster]

fine. that's still the cheapest way. the 750GB drives have the lowest cent per gigabyte. in that case, either settle for less storage or increase the budget. you want 3 tb. with 12 drives, it would be more expensive plus a lot more power and heat. think about that too.

 

[Bobthelost]

Originally posted by: ForumMaster
fine. that's still the cheapest way. the 750GB drives have the lowest cent per gigabyte.

No they aren't, a 400GB drive costs around $130, a 750GB drive costs $375 ish.

To the OP, a well thought out, interesting and well structured question. However i don't have a clue

*sits back with popcorn and waits for educated replies*

 

[d3n]

Multilane is just a bundle of cables I think. All of the individual cables should still be dedicated to each drive using a bundled connector. The SATA multilane 'feature' is just this way to save space on the connectors. This goes for the up and coming SAS too. Controllers manufactures kinda fuzz the issue of multilane I think becuase of the means that these SAS/hybrid SATA controllers use to address specific serial connected drives in a bus fashion like SCSI. The happy thing is this is far better than SCSI and really dosn't compare to in much in an other way. This is off the top of my head so dont take anything I just said to seriously.

You say you?d like to use a software raid 5 controller. I really don?t know how that would perform with 12 drives. Not to mention after a certain number of drives RAID5 reliability benefits fall off rapidly compared to a single drive especially on SATA vs SCSI. I really don?t know where the cusp is and I'd imagine it would be very debatable. I would be ok with 8 consumer grade SATA drives. Twelve drives especially from the same production run could be asking for trouble since more than one could fail within the same period of time.

I would suggest taking a look at the Dell 2900 rig. You could get a 2950 but I really like the value of the added PCI slots and drive bays in the 2900. It can be rack mounted and sometimes you can even get a hardware SAS controller bundled for no costs. Base configs seem to stick around $1800. That does not include the drives. You can add your SATA drives to this with the same 4x multilane cables. It has internal storage for up to 8 drives (10 if you use the 5" bays) you can get one CPU and upgrade to two later. I like the offload capabilities of the NIC for using ISCSI to map other systems to the storage array. On top of that with the SAS controller it has an external connection where you can add a whole other JBOD shelf with up to 7.5TB across 15 more drives.

These JBODs can chain together for up to 48TBs of space. Currently the only JBOD model that Dell has is the MD1000. Hopefully soon they will come with one that can be shared between two clustered storage servers. Not required at all for home or small office use really. I can see this saving a companies unbelievable amounts of money because then no one would ever have to think about a over the top SAN solution and the price that goes with it because this thing would smoke it.

Personally tho, I recently bought 10 of the 400Gig Seagate 7200.10 drives to completely redo my storage setup for about $0.29 per GB on a dead deal from outpost. I have one system with 4 drives in it configured in two RAID 0 sets. One set for the OS and the other set for caputuring and editing Video.

The storage server has 6 drives. One for the OS, one spare, and the other 4 on a Highpoint 1740 software Raid controller set up in RAID 5 for 1.09 TB of usable space. I have the chassis space to expand the array up to 8 drives. Otherwise I would have picked up the 2900 myself I think.

 

[MerlinRML]

I have not actually seen an external SAS multilane connector yet, but I've seen pictures. It looks like an infiniband connection, and my understanding was that a 4x multilane connector would provide ~12Gbps throughput, to give you 3.0Gbps for each of the 4 drives on that channel. You need 3 multilane connections, one to go to each set of 4 drives, for the total of 12.

Multilane should not impact whether you see the drives individually or not. Multilane is strictly the physical connection. Whether or not you see all 12 drives will depend on whether or not there is a controller built into the array. If there is, you may be able to disable it or put it into JBOD mode. If not, you can create 12 RAID 0 stripes consisting of 1 disk each. You've effectively bypassed the RAID controller, although I don't recommend it personally.

From looking at the drive array you indicated, there is no RAID controller built into the array. The RAID support is provided entirely by the host controller. Is there a reason you don't want a disk array with an onboard RAID controller? I've used some from ADTX and been pretty happy with them. It may be more than you're looking to spend, though.