The Seagate 3TB drive - the real thing

...or how to upgrade your iMac/MacPro hard drive to 3TB and get a external FireWire 800 enclosure for your Mac for free

We can‘t have enough disk space in our Mac. In our times, we store everything digital. We download our favorite movies and the latest albums from iTunes, take pictures and videos of our beloved ones (or for work) with digital cameras and transfer that to our Mac. There are business papers, presentations, eMails - you name it. Nearly everything in modern life can be represented by a file, and so we permanently increase disk space to keep up with the need to store these huge amounts of data.

Hard drives store their data into tracks, which is a circle on the surface of the rotating platter. A track is divided into sectors, where the actual data is stored in blocks of 512 Byte (or multiples of that), which are the smallest part of the disk you can access. A cylinder is the term for multiple tracks at the same position, but on different platters. As platters are build on top to each other and have data on both sides, you can address a Track by telling the hard drive which head you want access, and which cylinder it should move to. To access a specific sector, you then to access it by a number. So (50,1,4) accesses the forth sector on the fiftieth cylinder with the first head, now the hard drive knows which physical part of the drive it actually has to read or write. Newer hard drives physically don‘t correspond to that anymore, but use in software the same scheme to address sectors, to address bigger hard drives, 255 possible heads are used, even if there are only 8 physical ones. They get remapped to parts of the disk in the software of the hard drive's controller.

This addressing scheme was limited to 255 heads, 65 sectors per track and 1025 cylinders. This allows a maximum disk space of 255*65*1025*512 bytes to by addressed, or about 8GB. To make hard drives larger, the manufacturers increased the number of accessible cylinders to 16328 but limited the number of heads to 16. This increased the accessible space to about 127GB.

To overcome this, a different addressing scheme got invented, called LBA. LBA is just an ongoing number, which gets allocated to a specific block by hardware inside the drive. (Cylinder 0, Head 0, Sector 1) is actually LBA 0, (0,0,255) = LBA 254, (0,1,1) = LBA 255 and so on. The LBA however is limited to 32Bit, which is only capable of addressing 2048GB, or roughly 2.1TB. The BIOS of a PC runs in 32Bit, so there is no way address more space.






READ ON HERE IF YOU DON‘T CARE HOW A HARD DRIVE IS ACCESSED:
You might wonder why I‘m blathering about cylinders and heads and sectors and bits and bytes. Hard drive manufacturers haven‘t started yet to sell drives bigger then 2TB because virtually every PC uses a BIOS which can‘t address them (users with motherboards which use an UEFI may be <1%).
However when Apple introduced their Intel Macs, they included UEFI as a modern replacement for the BIOS, as Intel has suggested over the last years even for modern PCs. It runs in 64Bit, so it uses 64Bit numbers, and can address a 64Bit LBA. This correspondences to 8 Zettabyte (8 billion Terabyte) with hard drives who use 512 Byte sectors.

Seagate now introduced world‘s first hard drive with 3TB, the FreeAgent GoFlex 3TB. It‘s an external hard drive, so that Windows PCs can use the space. If you look inside, it‘s just a regular 3,5" 7200RPM SATA 6GBit/s drive.

As stated earlier, Macs don‘t have issues with drives larger then 2.1TB, so it will work just fine in an iMac or Mac Pro. If you are capable of changing an iMacs hard drive, removing the hard drive from the enclosure shouldn't be a problem for you. You can put your old hard drive inside the enclosure, and you get a free external hard drive with it, as the FreeAgent is about the same price as a comparable 2TB stock or external one with FireWire 800. However you need to purchase a base with an integrated controller to use the Seagate enclosure with FireWire 800 or USB 3.0, if Macs are going to support that. The enclosure has the ability to be upgraded to any other oncoming connection standard, as well.


Stock 3TB hard drives are about to be available at the end of 2010, so this is the only - and cheapest - way to get a top-of-the-line hard drive until then. The drive is around $200 plus $40 for the FireWire 800 base. If you don't live in the USA you want to order it from there. In Europe the drive is around 350€ (=$452), you'll get the drive for around 200€ (=$258) including shipping from the USA.

This stuff is just FYI. Correction and critics are welcome, it's a little unprecise but that's basically how it works. As well as zooming into MBR and GPT - oh, and excuse my bad english, the main purpose of writing this stuff is to improve it.

Regards

Hellhammer said:

Hmm... 250$, not that bad though 2TB externals go for as low as 110$.

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It's listed on newegg for 220$. I stated "comparable", which means no EcoGreen stuff, but 7200RPM drives. The Western Digital Caviar Black 2TB is $180, the Seagate Barracuda XT $200. There is one Hitachi drive for $130, but it has half the cache the other drives have, and is slower.
I think even the $40 for 1TB more space and a FireWire 800 enclosure is a great deal, just a comparable enclosure is about $50 or more.

Damn, I totally forgot the external 2TB drives. The Seagate 2TB 7200RPM external drive is $110, but 5900 RPM and only has 16MB of cache. The Western Digital 2GB external drive is more comparable, 7200 RPM, and it's $130. I don't know if I can trust those 3rd party specs, but the 3TB drive is definitely the actual 7200RPM desktop model, just wrapped up into an enclosure so that it can be sold without having only 2TB accessable.
It makes the whole thing not profitable until the 3TB-drive drops to <$195, at least in terms of GB per $. The enclosure seems nicer than the ones of the cheap hard drives, though.

Right, you need to get the base for FW800, so this thing is $250 total. The cheapest 2TB drive with FW800 is $190, and it's most likely some slower spinning eco hard drive. Also, the Seagate enclosure seems to be the most sophisticated out there, as it can be upgraded to USB 3.0, even faster then FW800.
I corrected the first post.

Problem is that nowadays external hard drives can be cheaper then the stock drive it contains. This drive is $210 with 3TB and a really cool enclosure. The same drive with 2TB without an enclosure is $200, that's why this thread exists.

Sure, but 4K sectors only push the limit to ~16TB rather then 8 billion TB (or 64 billion TB with 4K sectors). Also, first-gen drives use an emulation layer to split these 4K into 8 512 Byte sectors, which makes the same 2.1TB limit.

As long as you use a BIOS and/or MBR, you're not going to use anything else then 512 Byte sectors. May it be emulated or native, everything else is not supported and requires UEFI and GPT, and they support 64Bit LBA anyways so you don't do this to increase the accessible data. What they call "Advanced Format" is actually called "Advanced Format 512e", with 4K sector size on disk, but software emulated access via 512 Byte sectors.

If you use 4K sectors on disk and access it with a interface which is able to actually fetch 4K sectors, it increases the transfer rate because you decrease metadata by factor 8. Also, you increase the usable data on the filesystem from 86% to 94%, for the same reason. That's where the benefit is in that technology.

The emulation is inside the drive itself, it acts like there were 512 Byte sectors on the disk, but physically they are 4KBytes. Second-gen drives will report themselves to the system as capable to use 4K sectors, and if the system can't use them, it'll go into emulation mode. These drives aren't available yet, though.

APM and MBR can both only address 32Bit LBA and 512 Byte sectors, so do old chipsets and boot roms, they're limited to the same 2.1TB. You should be able to mount GPT formated drives with PPC Macs, but you can't boot them. At least if you run anything after 10.4.4.

There is a technology paper, which explains the Advanced Format stuff very well.

And who's gonna update that driver to correctly detect a sector size of 4K and not set the table up to default 512 Bytes, and do additional communication with the drive to not turn on 512 Byte emulation for Tiger and Leopard in 2012-2013 or whenever they're going to release these second-gen 4K drives? That's the point. We'll have 10.7 or 10.8 by then, you're lucky if these drives work correctly in Snow Leopard.

And no, with "Advanced Format" you can't access 4K sectors. All you get is emulated 512 Byte sectors. That is the only behavior first-gen 4K drives know.

For external hard drives you can use GPT. Best things you can throw into you Power Mac G5 are WDC VelocityRaptor 2TB drives when they're going to release them. SATA-I is to slow to benefit from SSDs, and the Raptors are going to be cheaper.

A) Block 0 contains the information from the driver about the block size of the drive. Most host drivers only support 512 Bytes. The OpenFirmware device drivers may do the same and thus the drive is not bootable, either. After this Block is read, the system is able to read the APT which contains the blocksize of it's partitions. If the driver screws up and reads 512 Byte blocks by default for a SATA attached hard drive, you can set it to whatever you want, it'll just ignore that setting.

B) Even if you could find a driver which works correctly, with an average disk size increase of 44% per year, those secong-gen 4K disks have to be available before 2014-2015 so they won't blow the 16TB limit. If your even luckier, some companies will provide legacy drives <16TB. How many iMac/Power Mac G5 with SATA were sold? Windows PCs will use UEFI and GPT by then, and BIOS based systems with MBR use a fixed blocksize of 512 Byte.

"DKIOCGETBLOCKSIZE" returns the block size which is stored in Sector 0. That is reported by the driver. The APT itself has no argument to set the sector size. If the driver reports 512 Bytes for every hard drive regardless what sector size it's using, you're screwed. Is there a DKIOCSETBLOCKSIZE? If not, you're screwed.

Read "The Structure of Block Devices".

They may introduce SATA 12GBit/s and make that mandatory to support sectors >512 Byte, leaving SATA 6GBit/s with the 512 Byte sector emulation → screwed. They may abandon SATA and introduce some new, faster connection and do the change with that → screwed.

You might want to ask a storage driver developer or somebody with a crystal ball.

We're talking about issues with SATA I device drivers, not SCSI drives. The "Structure of the block device" is what you actually refer to as APT.

SATA I Specification said:

A sector is a uniquely addressable set of predetermined size, usually 256 words (512 bytes).

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That's the drivers assumption, a SATA drive uses 512 byte sectors. Hard coded inside the driver, this is where the actual issue lies. Not inside the APT. The drive can report "I'm using 512 byte logical blocks on 4kByte physical blocks with an LBA alignment of X", but it won't be asked for that because in general, in those days, hard drives had 512 byte both logical and physical sectors and didn't need to be aligned nor accessed with larger sectors sized.

The Linux kernel does support these drives for some month now, so does Snow Leopard and Windows 7.