SAS vs. SATA, what’s the difference?
The abbreviations may look similar, but they’re vastly different technologies.
Both are types of hard drives commonly used in servers, and each has benefits and disadvantages.
Choosing the right drive is critical, especially when you’re hosting important sites or projects. This is one area where you shouldn’t make choices based solely on price.
What is SATA Storage?
Serial ATA (SATA) is the current evolution of the ATA hard drive from the 1990s and early 2000s, as used in home desktop computers. All computers sold today come with SATA-II or SATA-III, now often with SSD.
What are the benefits of SATA storage?
1. Cheaper than SAS
SATA drives are generally 75% less than comparable SAS drives.
So hosting providers can offer more storage space at a lower cost – or at a higher profit margin.
And dedicated server customers can take advantage of larger storage, such as backup drives.
2. Sequentially fast
SATA is really good at writing sequentially.
It’s capable of 6 Gbps throughput, and can actually write at that rate, if no random reads/writes are involved.
3. Good storage for infrequently-accessed data
The perfect use for SATA is storage for files, images, media, or backup snapshots.
A large RAID-protected SATA-based array will work well, as the writes/reads are mostly sequential.
What are the disadvantages of SATA stage?
1. Bad random read/write performance:
If SATA drives were cars, you wouldn’t be able to take corners like this!
In the world of storage, random read/write seeks and latency is analogous to the cornering ability of a race car on a track.
Taking the turn is harder than the straightaway (sequential).
A SATA drive simply crawls on random read/write request.
2. Uses the CPU
SATA does not have an enterprise-class method of managing data like SAS. SATA offloads data flow management to the CPU.
This means that disk I/O spikes heavily impact the system load average.
Shared hosting customers will especially feel the sluggishness on a SATA server, as dozens or hundreds of clients access it simultaneously.
SAS, by contrast, uses command queuing which is much faster.
3. Lower MTBF
And lower is worse.
The mean time before failure (MTBF) of a SATA is less than half that of SAS.
A typical SATA is 700,000 hours at a relatively cool 25 °C, while SAS is 1.2 to 1.6 million at a warm 45 °C.
4. Slower RPM
SATA drives commonly spin at 5.4k RPM whereas SAS drives spin up to 15k RPM
SATA is slower, and it affects performance.
The faster a disk platter spins, the faster you can read/write data.
Consumer-level SATA operate at a mere 5400-7200 rpm, while enterprise-class SAS operate at 10000-15000 rpm (twice as fast).
What is SAS Storage?
Serial Attached SCSI (SAS) is the current evolution of the SCSI interface drives used in higher-end workstations and servers.
Like consumer desktops, most modern servers come with HDD or SSD – but faster and more reliable.
It’s the de facto standard used by enterprises (including EuroVPS).
Below are a couple of pictures of some of our favorite SAS hard disk models!
Pictures of enterprise SAS storage
What are the benefits of SAS storage?
1. Faster Throughput
SAS drives can read/write and process data in a fraction of the time as SATA – especially on random reads/writes, and especially with the latest 12 Gbps disks using the latest RAID hardware controllers.
Although SATA is good at sequential data, random IOPS are terrible.
2. Better suited to 24/7 workloads:
SAS is made for servers, and often have 100% duty cycles.
Unlike SATA drives for your home desktop, which have 20-30% duty cycles, SAS is made to read/write data all day, every day.
SATA failures are also unpredictable by comparison.
In the SATA vs. SAS reliability war, SAS storage wins hands down.
Disadvantages of SAS Storage
1. Less storage capacity
SAS disks come in smaller size formats than SATA.
Common SAS storage sizes are:
- 73GB
- 146GB
- 300GB
- 450GB
- 600GB
- 900GB
- 1.2TB
- 3.8TB
For data archives, backups, or file storage, SATA is probably better but for production website content, SAS is better.
2. SAS drives have a higher cost
SAS drives are about 4x more expensive than equivalently SATA.
With the cost starting at $1/GB for enterprise SAS, it’s easy to see why most hosts only offer SATA as the default choice for their dedicated servers.
3. Higher power consumption
SAS uses more power than SATA. A SAS drive can use at least two times as much signaling voltage than a SATA or ATA drive.
More power means higher running costs.
Do most hosting providers use SAS or SATA?
Most professional hosting providers use SAS storage versus SATA storage for production data – especially for high I/O applications or mission-critical websites that cannot risk downtime, data loss, or data corruption.
Unfortunately, there are still many web hosts that advertise large disk quotas instead of delivering performance and reliability.
These are usually inexperienced, amateur or just plain greedy providers – many of whom don’t have experience working with large-scale storage. They’ve not (yet) seen the risks of cheap storage. It’s a huge mistake!
SAS vs. SATA: Final take away!
SATA may be fine at home, or on a cheap server, but it’s just not acceptable for use by mission-critical focused hosting providers.
EuroVPS has been using SCSI/SAS Storage exclusively since it’s founding in 2004, and in our experience, we’ve seen that 95% of server IOPS are random.
Using SATA would cause our servers to crawl and we’d be replacing failed drives non-stop. We don’t want that, and neither should you. Sites like WebHostingTalk.com are filled with countless horror stories of SATA failing from things like parity errors on the software RAID.
The easiest way to prevent this type of failure is to avoid it altogether. That’s why we now use SAS, always have used SAS, and always will use the best enterprise storage solution available. Your data matters to us.
Ultimately, using SAS storage will reduce risk or data loss, prevent performance issues, and just overall reduce hosting-induced headaches (for both the customer and the host).
