matheweis
asked on
SATA/SAS vs plain SATA; Cost Per GB - What am I missing?
Hello all,
I am looking to upgrade our current storage systems in a few of our locations from about 300-500 Gb to 2-6 Tb.
Everyone that I talk to tells me I should go for a high end, but basic, SATA RAID array using a few 500Gb disks. If I start talking scalability, they start talking about fiber channel, but warn me against the high costs involved. Every time I mention SAS, I get warned against it, for it being either more expensive and complex than FC, or just that it's a "fancy new toy, but not as good as FC".
I feel like I'm really missing something here....
It looks to me like, assuming I am going simply for capacity and not extremely high availabity, that I should be able to host, on a single 8 port SAS card, an array easily scalable to over 60 Tb of storage for around $0.58 per Gb. (*) What's more, it appears that the overall cost will scale in a linear manner if I need more or less storage space...
(*) Assuming the following:
1 eight-port SAS card: ~$1000
8 12x SAS Edge Expanders: (1 host <-> 11 devices) ~$8000
88 750Gb SATA disks (**): ~$25000
11 basic 8-disk SATA ensclosures: ~$2500
Misc cabling and adapters: ~$2000
Total: $38500
Storage: 66000 Gb
Cost per Gb $0.5833
(**) I'm going with the assumption that you CAN use SATA disks within an SAS array... Everything I see in the specs indicates that you can, and since I'm only looking at capacity, I don't need the dual-port redundancy available to SAS drives.
Note, of course, that I only need 2-8 Tb in my arrays initially, something that can easily be taken care of with a standard SATA RAID controller. But I like the idea of being able to scale... The entry costs to SATA and SAS appear very similar when using SATA-only drives, and the overall costs appear to scale in a linear manner.
What am I missing? Why do OEM builders and other sysadmins shy away from SAS? Is it just because SAS equipment is so new? Is there something unusual about the way SAS cards interact with their arrays?
I can build the array I noted above, right?
Any input would be appreciated; thanks in advance.
I am looking to upgrade our current storage systems in a few of our locations from about 300-500 Gb to 2-6 Tb.
Everyone that I talk to tells me I should go for a high end, but basic, SATA RAID array using a few 500Gb disks. If I start talking scalability, they start talking about fiber channel, but warn me against the high costs involved. Every time I mention SAS, I get warned against it, for it being either more expensive and complex than FC, or just that it's a "fancy new toy, but not as good as FC".
I feel like I'm really missing something here....
It looks to me like, assuming I am going simply for capacity and not extremely high availabity, that I should be able to host, on a single 8 port SAS card, an array easily scalable to over 60 Tb of storage for around $0.58 per Gb. (*) What's more, it appears that the overall cost will scale in a linear manner if I need more or less storage space...
(*) Assuming the following:
1 eight-port SAS card: ~$1000
8 12x SAS Edge Expanders: (1 host <-> 11 devices) ~$8000
88 750Gb SATA disks (**): ~$25000
11 basic 8-disk SATA ensclosures: ~$2500
Misc cabling and adapters: ~$2000
Total: $38500
Storage: 66000 Gb
Cost per Gb $0.5833
(**) I'm going with the assumption that you CAN use SATA disks within an SAS array... Everything I see in the specs indicates that you can, and since I'm only looking at capacity, I don't need the dual-port redundancy available to SAS drives.
Note, of course, that I only need 2-8 Tb in my arrays initially, something that can easily be taken care of with a standard SATA RAID controller. But I like the idea of being able to scale... The entry costs to SATA and SAS appear very similar when using SATA-only drives, and the overall costs appear to scale in a linear manner.
What am I missing? Why do OEM builders and other sysadmins shy away from SAS? Is it just because SAS equipment is so new? Is there something unusual about the way SAS cards interact with their arrays?
I can build the array I noted above, right?
Any input would be appreciated; thanks in advance.
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mafo:
I've seen and read the referenced whitepaper, which has helped me to come to the conclusions noted above. I see your point about SAS reliability, though I would point out that it has little to do with the SAS vs SATA protocol, and everything to do with the actual quality of the drives as manufactured. See my response to andyalder below:
andyalder:
Yes, the drives are high end drives sold by Western Digital, advertised as 'server class' and/or 'enterprise class'. They appear to use components akin to the high end SCSI or SAS drives such as fluid dynamic bearings. They have an 5-year warranty, and an MTBF of 1 to 1.2 million hours. I am unable to find an AFR, but other SATA WD drives (Such as the Caviar SE series) have an AFR of < 0.5% I also read that all WD drives are manufactured to an AFR of < 0.8% The bottom line is that these cannot possibly be drives that will be failing at even a rate of even 1 out of 100 after 2 or 3 years; it would be disaster for Western Digital from a business standpoint.
Take a look:
http://www.wdc.com/en/products/products.asp?driveid=331
http://www.wdc.com/en/products/products.asp?driveid=335
eagle0468:
Thanks for the added info.
A few final comments:
My main question was if there was any reason to choose between an SATA controller running SATA disks, or an SAS controller running SATA disks. Hearing such comments as SAS being only a fancy new toy scared me away a bit. However, as I saw it, SAS could do everything SATA could, with much more capability.
My 66Tb disk array was only a theoretical demonstration of the capabilty of SAS. As noted before, my actual intent is only to build a few arrays (in different locations) of between 2 and 6 Tb. Using 500 Gb disks, that's a max of 12 disks in the array using full RAID 10. Therefore I don't see that I would practically be replacing a couple of disks per week, since replacing 12 disks would replace the entire array. (And in practice, I am looking at RAID 5EE, so that would only be 10 disks)
The biggest point I was looking to verify is that the cost per Gb using the SATA infrastructure vs the SAS infrastructure are virtually the same, while the SAS infrastructure allows all the same capability of SATA with far greater expansion and capability in every aspect.
Thus, it would be pointless to purchase of an enterprise level SATA RAID controller since the cost of an enterprise level SAS and SATA controller is more or less identical. (~$800)
Thanks again for all your input.