Introduction
Greetings. I want to discuss Direct Attached Storage (DAS). What it is and why you might need it.
In my current situation I am living off a laptop, with a couple of DAS devices. Both devices cost about the same. However one is solid state and much faster. The other is mechanical and much larger.
Probably, the vast majority of people using computers may only need DAS, and not any sort of network solution.
Flash Drives have gotten very large lately. They sort of took over DAS from cdrom/dvrom once they hit 8 GB and bigger. And I know people who use flash drives, and SD cards, as many laptops have a SD slot built in.
There are external hard drives. TB of inexpensive storage. One just needs to chose between mechanical and solid state. Solid state is faster, but mechanical is still cheaper per GB.
Then there are a wide variety of options for using internal drives externally. USB to SATA, and multi bay drives, some even supporting hardware RAID. Though these options loose something in the form of portability.
Overview
Let me start by defining what I mean by Direct Attached Storage or DAS. Basically any sort of data storage device that is external or separate from your computer, and is directly plunged in though one of your computer ports.
And by any sort of data storage device, I do mean anything. On my old commodore 64 I used a cassette deck connected through the serial RS-232 interface as a DAS. External Floppy drives can also be classified as DAS drives (again using the Commodore 64 as an example).
A DAS should be able to do two things. It should be able to save data external to your computer and it should allow retrieval of said data back to your computer. Technically a paper tape punch could be considered a DAS. While not very efficient it fits my functional description (barely).
Of course this was back in the day before home networks or the personal LAN (Local Area Network). Back in the day NAS was not even a dream for most computer users. But that is the past, and we want to look at the here and now, what DAS options are available, and why you might want to use one.Since we are talking about the modern day we can eliminate a number of methods of direct connecting storage to your computer. We will focus on what the most common connection types are. And this basically comes down to USB. I need to also mention Fire Wire, thunderbolt, and eSATA, Though it looks like USB is the present and future.
Note I am not counting memory cards like the SD standard, as either you have a port for direct connect (which is probably USB under the hood), or you are using a USB Dongle, in which case it falls under USB connections.
Another issue I want to discuss is throughput or speed. This is basically a measure of how fast you can move data from one place to another. Unfortunately it is not as clear cut as it should be. Odds are if you have been using a computer for awhile, you have connected a high speed device and wondered why is this thing so slow? We will take a look at throughput as part of our discussion.
USB Devices
USB is by far the most common connection type for DAS. It has been around since the 1990’s, and has gone through several updated and iterations. And to add to the confusion there are a number of (I think about 20 last time I counted) different connectors of different shape and color.
There are currently four generation of USB, with several sub generations. USB 1 came out in 1996, while USB 4 was released in 2019. Initially USB took a back seat to other connection types, as USB 1 had transfer speeds of 12 Mbs or slower. However speeds have increased over the years with USB 4 capable in some cases of 80 Gbs speeds.
USB is also an industry standard not belonging to any corporation. It is managed by the USB Implementer Forum.
You may notice, if you poke around the internet, a lot of commentary on the unreliability of external USB drives. It is not unheard of for an external USB to drop connection for no obvious reason, leaving your file copies in a questionable state. So I want to quickly address some issues to be aware of if you are experiencing USB dropouts.
- Loose or faulty cables and connectors
- Insufficient power
- Outdated or broken drivers
- Power saving settings
- Overheating of USB chips on external device
- Software conflicts
- File system Errors
- Actual physical damage
The main word of caution here, do your research on an external USB drives and Enclosure, as some USB implementations are not as robust as others.
eSATA Devices
eSATA is a variant of SATA, with the “e” standing for external. It was introduced in 2008. Since most external drives within their cases have a SATA interface that needs to be translated to USB, eSATA has certain advantages in that it needs no additional translation.
There are some issues with eSATA that limited its usage. Unlike USB, eSATA cannot provide power, thus requiring an external power supply. This was not a big issue for larger enclosures which would draw more power than USB could provide. However a single 2.5” drive could easily be powered off USB, but would require separate power with eSATA.
The other issue was that eSATA came out at about the same time as USB 3. While eSATA is faster than USB 2, USB 3 quickly surpassed eSATA throughput.
The eSATA port is more common on older computers, but has pretty much been replaced by USB 3, USB 4, and Thunderbolt on newer computers.
Firewire Devices
Firewater was developed by Apple in conjunction with several other tech companies. It is primary known from iphones and ipods. Needless to say firewire is not an open standard by any means, and never gained much traction outside of Apple products.
While Firewire has a higher transfer rate than USB 2, it has been outpaced by USB 3 and USB 4, as well as thunderbolt. In point of fact newer apple devices have abandoned Firewire.
It is also harder to find any non apple products that support Firewire. Because of this its use in DAS is limited to mainly Apple products.
Thuderbolt Devices
Thuderbolt was developed by both Intel and Apple. Thunderbolt 1 was introduced in 2011. The latest version is thunderbolt 5. Interestingly, USB 4 is based on Thunderbolt to a large extent.
Thunderbolt combined PCI Express and Display port technology. Thunderbolt 1 and Thunderbolt 2 used the mini DP connector. Thunderbolt 3 and beyond use the standard USB C connector.
In terms of DAS, you will not find a lot of Thunderbolt in use. Mainly because of the cost, as compared to USB. It is mainly used in higher end equipment.
Use Case for DAS
Direct Attached Storage provides external storage. There are many reasons you might want external storage. One of the primary reasons for many people is backups. Related to backups but with somewhat different use cases is archives.
We carry around a lot of personal data on our computers. And in many cases it is data we rarely use, but need to keep. This tends to lead to our internal computer storage filling up. And in many cases moving said files to a Direct Attached Storage device can free up storage space. Not to mention being somewhat simpler than upgrading internal storage space.
For many of the tech savvy out there, you will say that is easy. However there are lots of non tech savvy users out there, and plugging in external storage is less intimidating and generally easier.
DAS works great for a single user with a single computer. Where NAS comes in is with multiple users and multiple computers needing to access the same data at the same time. If that is not you, then DAS is probably a better fit.
Another advantage of DAS over NAS. When you are not using it, unplug it and set it on the shelf. Whereas a NAS is always on the network and may be subject to hacking (depending on your network polices). A DAS, when not in use, requires physical proximity (some one has to actually pick it up physically and connect it).
And one more reason for using a DAS is speed plain and simple. A direct connected device is always going to have faster throughput than a network connected device.
The big down side of DAS, they have to be physically connected to the computer to work.
What to Look for in a DAS
The first thing to consider when looking at DAS, how much data do you have?
I have used CDROM and DVDROM for external storage in the past. Though nowadays our storage requirements have expanded. If your computers main storage drive is 10 GB, using a DVD ROM makes sense. It does not make much sense if the drive is 100 GB or bigger.
By the way, you can get 128GB plus mainline USB thumb drives for $25 US dollars or less now days. And this may be fine for a lot of people if you do not have a lot of data to store. In fact you can get USB thumb drives up to a TB now days. Just be aware there are a lot of knock offs advertising mass storage for very cheap prices. You know what is said a about something being to good to be true, it isn’t. Stay away and stick to the main line USB manufacturers.
The next step up is a external storage drives. Solid state or mechanical. Any 2.5” drive or any solid state drive will work fine off USB power. Three and a half inch drives will probably require external power adapters.
And the final level is a multi drive enclosure, which defiantly requires its own power supply. Some external enclosures even have hardware raid built in.
Cautionary tale
One thing you want to be concerned with, especially with long term storage, is how well the various media retains data. Unfortunately there is not a lot of clear cut information out there, and some of it can be contradictory.
Mechanical drives use magnetism to store data, and this can fade over time. Plus they can be prone to mechanical failure. Flash Memory uses charges, which can also fade over time. Additionally flash memory can only accommodate limited amount of writes.
The only real advice I can give is don’t cheap out on devices meant for long term archive and backup storage. And schedule periodic checks of your data. Also do periodic data refreshes on your storage media.
There are lots of recommendations out there for refreshing data. So it is well worth researching. As a parting example, here is what I do with my backups.
I have about 1.45 TB of data I need to keep backed up. However I find that amount of data slowly expanding over time. I have a couple 4 TB drives, just to be on the safe side, used for nothing but backup. I run a rsync backup server with an external two drive enclosure. I do normal backups to one of the drives. Each year I install another drive and clone my backup drive, thus refreshing all my data. Then I used the cloned drive for a year. Since this all happens on a backup server, it does not really affect my normal operaitons.