Choosing Hard Disks

For the purposes of video editing it used to be de rigueur to have expensive SCSI drives. That does not apply anymore. With the advances in speeds of IDE drives and SATA drives - and the easy availability of RAID - the type of speeds required for video editing have become very affordable. This page covers the main non-SCSI options and links you to pages on RAID that will make your IDE or SATA drives run faster than if you had SCSI disks.

What to look for in hard disks:

Terminology

Hard disk technical specifications include the following terms: IDE, SATA, Seek Time, Peak Transfer Rates, sustained throughput rates, DMA, spindle speed in rpm, disk cache, number of platters, and - for SCSI disks - LVD, Ultra 160, Ultra 320, etc. Hard disks can be cabled together/configured as stand alone drives, RAID 0, RAID 1, or a combination of RAID 0 and 1. (There's also RAID 5 and RAID 10 but we won't go into that here).

IDE / SATA

PCs have had IDE hard disks for many years now. More recently however there have been big improvements in IDE speeds and capacities. A newer format is the SATA or Serial ATA drives. They use a different data cable and different power cable to connect to the rest of the PC components. Make sure your motherboard supports SATA or you may have to buy a PCI card that provides a connector to plug your SATA drive into. SATA drives show up in the BIOS and in Windows as SCSI drives just to confuse you :-)

Cables

IDE disks use ribbon cables that are either 40 pin (UDMA 33 and below) or 80 pin - that's just what they are called, the plugs look exactly the same though. SATA drives use a special SATA cable. SATA drives also require a different power plug to the standard Molex used for IDE disks. Do check that your Power Supply Unit (PSU) does have that type of output or you may need to buy a Molex to SATA adapter.

DMA

Ignore the DMA descriptions that you get with the IDE and Serial ATA (SATA) drives. Ultra DMA 100 (UDMA 100) has a theoretical maximum data transfer rate of 100 megabytes (MB) per second. That never happens. Similarly UDMA 133 and UDMA 150 don't give you 133/150MB per sec. More important is that when using anything with a DMA above 33 make sure your motherboard (or IDE controller) supports that speed, that you have set it correctly/enabled it in the BIOS, and do use the correct 80 pin IDE cable, or your disk will default to a lower speed. If using a Windows operating system prior to Windows 2000 ensure that you install the PCI bus controller software to ensure best speeds. Whatever version of Windows you are using ensure that the hard disk shows up in the Device Manager with DMA enabled. 

Disk RPM

Never use a 2.5" IDE hard disk. These are typically used in laptop computers and tend to be much slower than the ones used in desktop PCs, even as slow as 3200 rpm. Also, never use a 5400 rpm disk. They just don't have the speed required for video editing.

With 7200 rpm and 10,000 rpm disks available in IDE and SATA at very affordable prices there's no reason to settle for 5400 rpm. 

Cache

Cache is basically RAM that exists on the hard disk itself. Windows accesses data in the cache before it looks on the hard disk for what it wants. A hard disk that holds more data in cache is going to be a lot faster as accessing data from RAM in a few nanoseconds is a lot faster than accessing data from hard disks in a few milliseconds. Standard IDE hard disks hold 2 MB of cache. Faster IDE disk and SATA disks hold 2 MB or 8 MB. SCSI disks tend to hold anywhere between 2 MB and 8 MB of cache.

Number of platters

Platters are the magnetic disks on which your data is stored. Hard disk have reading heads that find the location of data on the platters. The less the head needs to move to find the data the quicker the drive is going to be, but a detailed discussion of platters is outside the scope of this article and not really a major consideration at this point. 

Seek Time / Peak Data Transfer Rates

The maximum theoretical rates are a waste of time. What a hard disk is capable of under a strict set of conditions is not what you will get in normal use. The important consideration for you is the sustained data transfer rate. If the sustained throughput drops below what is required for your video you will end up with jerky results and dropped frames. 

To a certain extent the Seek Times do matter. As the name suggests this is how long the hard disk takes to find the data in it's store. Really fast SCSI disk have rates under 4 milliseconds.

Ideas / Suggestions

• When you have a choice of formatting your drive in FAT32 (File Allocation Table) or NTFS (New Technology File System) always go for NTFS. There's a 2 GB AVI file size limitation in FAT32 that can cause you a lot of problems.
• Setup your hard disks in RAID
• Use an IDE caddy. An internal one will fit in a 5.25" drive bay and has a removable tray into which you can connect a hard disk. When the disk is full it's a simple matter of removing the tray and replacing the disk with a new one. 
• IDE caddies are also available in external units. When using an external one ensure it connects via firewire, or - at the minimum - USB 2.0. Strictly avoid older ones that connect via a serial or parallel port.
• Don't fill your hard disk. As you put more and more data on a disk it gets slower and slower. Leave at least 20% of your hard disk free AT ALL TIMES.
• Run a regular defragmentation from Windows > Accessories > System Tools. If you are an advanced user get a swap file defragmenter and defrag your swap file as well.
• Backup regularly, not only when you've finished your project but develop a habit of hitting Control + S on a regular basis to keep updating the backup of the project you are working on.
• Always go for more storage rather than less. If you are making a two hour DVD to fit on a standard DVD of 4.7 GB you'll probably need about 60 GB of hard disk space including your requirements for storing all the original "raw" DV footage, extra graphics, audio tracks etc. 
• Read these tips on getting the best performance from your hard disks.
• Enable Write Cache for your hard disk to improve I/O performance.
• For SCSI disks disable Tagged Queuing
• Disable Synchronous transfers. Synchronous transfer mode permits the sending device to send multiple data packets without receiving acknowledgment that the receiver actually received every data packet sent. As a result, more data can be sent/received before acknowledgement is required