We all know that in terms of reliability SCSI drives are superior to SATA, but how many of you actually use them in production servers? With the cheap cost of SATA storage now available, are SATA drives really worth the risk?
There are many differences in the interface technology and in the commands executed. SCSI has a robust tagged command queuing implementation to allow multiple commands to be outstanding which provides significant performance gains for drives or controllers by being able to order the commands in an optimal execution manner. ATA only allows a bus release that is mistakenly called command queuing. The implementation on the class of disk drives that support ATA is different as well.
ATA drives are cheaper than SCSI or Fibre Channel drives and there's a reason. SCSI and FC drives use a processor for executing the commands and handling the interface and a separate processor controlling the head positioning through servos. ATA drives use a single processor for both which means that if the rotational positioning requires more adjustments due to factors such as rotational vibration or wear, more processor time will be dedicated for that which can affect the performance of the drive. Because of this, you will usually see a lower RPM for the ATA disk drive and also a shorter warranty period. But it is cheaper and can be a very good, economical solution for many environments and applications.
It all comes down to your budget, if you are given a task and a budget where do you place the funds? more people use SATA RAID for their production server, since they have to replicate this setup over and over.
Thanks for the info. For mission critical applications such as web hosting servers, I am starting to feel that SCSI may be the only option in terms of reliability. SATA drives seem more suited towards general business applications and not for hosting servers (which if a drive fails and the system goes down) is a critical issue.
Taking this question further, possibly SATA drives are suitable for server applications if in a RAID 1 configuration, for example.
Your comments and feedback are appreciated as I am currently in a dilemma as to whether to provision a new batch of servers on SATA or not.
SATA drives come in higher capacity. I always go with SATA drives in a RAID-5 configuration (so if you do have a single drive failure, you won't miss a beat). If you want to minimize downtime, make sure the drives are hot-swapable (or have a hot spare installed).
I'd only go with SAS drives for a highly loaded database server or if you really need the I/O performance. For the database server, go with RAID-10 (at least 4 drives) as this will give you the best performance and recovery in the case of a drive failure. Note that you don't get as much usable space in a RAID-10 configuration as in a RAID-5 configuration.
I guess my main comment is that if you are worried about reliability, you really need to go with a Raid solution (even RAID-1 if you are on a tight budget) and not worry about the difference between SATA and SCSI failure rates. Raid goes a long way to increasing your reliability since both SATA and SCSI drives can fail on you (regardless of what the failure rates are - these are the moving parts in a server and they do wear out over time).
The application I am looking at is general web hosting, but with an emphasis on reliability. What are your thoughts on 4 x SATA drives in RAID 1 configuration? or is that an overkill and would this best be utilised as 4 x SATA in RAID 5 config?
I am concerned with RAID 5, it can take a long time to rebuild.
If you have at least 3 drives, always go with RAID-5 (which requires at least 3 drives). If you have 4 drives, you can go with RAID-10.
As for the rebuild, this is done on the fly with RAID-5 and you shouldn't notice any downtime at all if you have to replace a single drive (if the drive replacement is not hot swapable, the data center will have to take the server down to do the actual drive replacement). If you are worried about even that downtime make sure your provider will hot swap a bad drive or install an extra hot spare in advance you can add to the array on a drive failure in the array.
RAID-5 or RAID-10 is definitely the way to go for reliability. RAID-1 would be the choice if you only had 2 drives.
Maybe others with more experience than me will disagree, but I've always gotten RAID-5 SATA for general web servers and RAID-10 SAS/SCSI for high performance servers. I've never used RAID-1, but would if the server didn't allow more than 2 drives to be installed.
All comes down to your Business model & pocketbook.
I know I would get an excellent and much better vehicle for $60 - $80 thou, as opposed to $20 - $30 thou, but unfortunately, the first is outside the limits of my pocketbook and the second will suit my needs just fine.
There is a big difference in the cost / size of any SCSI drive compared to any SATA, which is what drives most people to use SATA drives, especially with SATA2 now available. SATA drives have proven their reliability and coupled with at least RAID 1, is an excellent setup for any production Server.
Remember also, one needs to always add a hard drive for backup regardless of whatever RAID setup is used.
• PotentProducts.com - for all your Hosting needs
• Helping people Host, Create and Maintain their Web Site
• ServerAdmin Services also available
Thanks for clarifying. Would I be correct in assuming that 2 drives in RAID 1 configuration would be just as reliable as 3 drivers in RAID 5 configuration?
Although I've never used RAID-1, it is my understanding that if one of the drives fails, you will need to rebuild the new drive before you can use the server. This can add some downtime especially if the drive needs to have 250GBs or more copied to it.
I could be wrong though. Maybe you can rebuild RAID-1 on the fly also...
With RAID-5, the rebuild goes on in the background using the data on the other drives to rebuild the new drive.
Note again, that I don't have that many servers and I have not had a drive failure yet (only been using dedicated servers for about 2 years). But, this is how I understand it.
Also, you don't want to rely on RAID for backup of your data. You should backup your data to at least a separate server in the same data center and probably another one in another part of the country (and from a different company just in case your provider decides to hold your data hostage for some reason or your provider goes out of business suddenly).
You want a backup copy of your server in the same data center if you need to get it back online the quickest in case of a server disaster.
Although I've never used RAID-1, it is my understanding that if one of the drives fails, you will need to rebuild the new drive before you can use the server.
Most RAID controllers can rebuild a drive without bringing the server down, regardless of whether it's RAID1 or RAID5.
As far as SATA vs SCSI, it depends on your budget and the amount of load you're going to be put on the server. SCSI drives perform much better than SATA in a server environment, but if the server will be lightly loaded, then you may not notice the difference. If you're looking for quality, and you can afford the price difference, then 2 SCSI drives in a RAID1 array would be a good option.