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-   -   Recommendations: external drive enclosure + RAID (http://www.linuxquestions.org/questions/linux-hardware-18/recommendations-external-drive-enclosure-raid-299850/)

Dark_Helmet 03-09-2005 10:56 PM

Recommendations: external drive enclosure + RAID
 
Real simple: I want an external tower to house a bunch of drives (don't have a rack, and don't plan to buy one). I'd like the enclosure to support SATA or SAS drives (I know, SAS would be very expensive to populate), with the capability of being controlled with or without a RAID controller. Support for 5+ drives/devices would be ideal.

Does anyone have any "war stories" of doing this either on their own or as a part of a job? Suggestions on the enclosure, a RAID controller, or general information would be welcome.

I want to implement this piece-by-piece rather than buying a "turnkey" solution from a dealer. Their systems are a bit expensive, and a bit limiting from the upgrade perspective. At least, that's my take on it...

twsnnva 03-10-2005 05:32 PM

External RAID is expensive, the major reason is connectivity. You can install a bunch of SATA or ATA drives in an external exclosure fairly cheap, but you will need somehow to connect all of these to your server. The most common ways are fibre channel and scsi. To do this the external enclosure will have a board so the SATA drives will show up on the SCSI, or fibre channel bus. Most of these boards will also do RAID. For this reason most external enclosures start around $5000, and this is only with a few drives installed. You will also need to have a SCSI or fibre channel adapter in your server, which will be another $300+ bucks. I would go with an internal RAID, using software RAID you can build a 1 terabyte RAID5 setup for around $500.

mrjag 04-10-2005 11:16 PM

What parts would go into a terabyte of raid5 for $500?

twsnnva 04-11-2005 05:22 PM

5 250GB HDDs, and extra controllers. IDE drives of this capacity are currently $102 on pricewatch and SATA drives are $112. Assuming you have one onboard controller, you would need 1 IDE or 2 SATA controllers, they are $9 and $12 respectively.

1TB IDE RAID = $519
1TB SATA RAID = $584

Dark_Helmet 04-11-2005 10:42 PM

To be fair, the prices quoted for IDE drives are for either bulk purchasing (the first item listed on pricewatch is a price for a quantity of 20 or more), or refurbished (the second entry on pricewatch is for a refurbished drive(s) with a 30 day warranty). For the SATA drives, either the first or second company listed quotes this at the bottom of the description:
Quote:

MDT reassembles hard drives using components outsourced from major brand hard drive manufactures ...
And that sounds very much like a component similar in nature to "refurbished". Not exactly the same, but leaves me with the same level of confidence as a refurbished part.

I would also have to assume that the controllers are also either refurbished or from smaller, less well-known companies. Parallel ATA is probably standardized to the point so much so that any mom-and-pop store can slap an industry standard chip on a card and it would be acceptable. For SATA, I'm not so sure. It's still new enough that I'd be hesitant to trust a no-name brand.

In addition to the parts listed above, there is, of course, the overhead of purchasing the case and components. That would probably easily add another $150 to the cost, but the tradeoff being performance. Software RAID may be cheaper, but it is very processor intensive. For RAID 5, a write to the disk requires the processor to recalculate parity. That requires a read from the drive itself DMA'ed into memory, a read from the corresponding parity stripe (also DMA'ed into memory; best case in parallel with the first read), the processor then XOR's the old data with the new to generate the new parity, and finally pushes both the new data & new parity out to the respective drives/partitions/stripes. In addition, you've got the cost of the operating system itself, including any device-sharing technology enabled (NFS, Samba, or whatever). So clearly, the faster the processor (and more memory) the less of a slowdown you'll incur. And of course, the faster processor and more memory will drive up the host system price.

I'm sure everybody can tell I'm not a big fan of software RAID. :) I'm also slightly biased. I work as a verification engineer for a company that develops RAID chips (on-board and via expansion cards). I'm not saying software RAID bad, but it's not really what I want. I just wasn't specific enough in my description. It may be perfectly suitable for everyone else though, or if budget is extremely crucial.

For anyone else interested in what I've come across, Kingston sells a line of "data silos" that fit the external enclosure idea: just a box to plug in drives, with a backplane for communication. They come in lots of different sizes, but as far as I can tell, are only available for SCSI-160, and maybe SCSI-320. Of course, you would also have to buy drives to populate it, and a RAID card with an external SCSI connection.

I know I said I didn't want a "solution", but I did come across an interesting box by Buffalo Technology. They call it a Terrastation. You can look at the three different models here. It's an external box with a 10/100/1000 Mbit network jack, RAID 5 capable, with 4 drives of varying capacity. The 1TB version offers 750GB of RAID 5 storage for $1000 (all new equipment; listed through their linked retailers) or 1TB of non-RAID storage capacity. I haven't figured out what types of drives it takes, and how easy/difficult it is to replace them. From the info I've read, it sounds as though it uses industry standard drives.

mrjag 04-12-2005 09:57 AM

Thank's guys, this will give me a starting point.

twsnnva 04-12-2005 05:11 PM

The terastation is just a box running some linux variation , for that price it has to use native software RAID. Also note it only has a 266 Mhz PPC CPU...if this box can handle RAID + filesharing + printsharing, a cheap 1Ghz x86 system can too.


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