STAR Watch Statewide Technology Assistance Resources Project A publication of the Western New York Law Center,Inc. Volume 9 Issue 2 March/April 2005
Hard Drive Capacity: How much do you really need?
Computer geeks will always advise over 200,000 digital photos or 33 that there is no such thing as a com- hours of raw video. That should take puter hard drive that is too big or too a while to fill up. fast. While those among us who use computers only for word processing Many people would like to upgrade the or spreadsheets may be satisfied with hard drive on their computer or pur- a hard drive capacity of 20 – 40 Giga- chase a new computer with a lot more bytes, there are some of us who need storage capacity, but become intimi- much, much more. For instance, dated by all of the acronyms and buzz- anyone who has ever edited a video words. It isn’t that difficult. There are will tell you that 3.16 Megabytes of only a few issues that need to be ad- disk storage is required to store 1 dressed. second of raw video. That translates into approximately 12 Gigabytes of SCSI vs SATA vs PATA hard drive storage for every hour of raw video, and doesn’t include any SCSI, SATA, and PATA describe how work/temp files or the final product. the hard drive is physically connected Many of us with digital still cameras into the computer. Each of these in- are also running out of space. While terfaces have advantages and disad- those new high-resolution cameras vantages that users should be aware produce excellent quality images, the of. None of these interface types are amount of storage space for each pic- ture can exceed 2 megabytes per pic- In this issue… ture. ? Hard Drive Capacity:
How much do you really With the latest products announced by hard drive manufacturers, it is need? now possible to purchase computer ? WNYLC Web Statistics hard drives that have a capacity of ? Who We Are up to 400 Gigabytes. With that amount of storage, users can store STAR Watch - 2 March/April 2005 compatible with any of the others. If specs of any manufacturer’s PATA you are upgrading a computer, you and SATA drives, it is very clear that must install the correct type of hard the physical storage device at the end drive, or be prepared to purchase of the data cable is the same. Only and install a new interface card to the electronic interface is different. connect the hard drive to the com- According to the published test re- puter. sults, SATA drives are slightly faster.
Typically, SCSI interface hard drives If the hard drive is going to go into an are most commonly found in file existing computer, it would be much servers and a few very high perform- better to use the same type of drive. ance workstations. Their perform- While it is possible to mix and match ance is somewhat better than PATA drive types or use different drive or SATA drives, but not their price. A types, it could get very complicated. SCSI hard drive costs 4 to 8 times as When upgrading storage on an exist- much as a PATA or SATA drive of the ing computer, stick to the type of same capacity. The typical computer drive that is already in the computer. user cannot justify the high cost of This is not an issue with new com- these drives for a desktop computer. puter purchases.
PATA, or Parallel ATA is also referred RAID (Redundant Array of In- to as IDE or EIDE. It is currently the dependent Disks) most prevalent hard drive type in computer workstations today. These While many people have gotten the types of drives are connected into the impression that RAID is just another computer by a wide, flat, ribbon ca- interface type like SCSI, PATA, and ble. Some critics argue that if these SATA, it isn’t. RAID provides a ribbon cables are improperly routed, means to connect multiple hard they can cause cooling problems by drives together to achieve greater blocking airflow to critical compo- storage capacity, better performance, nents inside the computer case. greater storage reliability, or any combination of the three. As such, SATA, or Serial ATA interface hard the subject of RAID is outside the drives have been available for at least scope of this article, except to say 2 years, and expected to outsell PATA that there are RAID systems for drives by the middle of this year. SCSI, PATA and SATA hard drives. SATA drives are connected to the computer by a thin interface cable A Word About “Drive that cannot block airflow inside the Speeds”… case.
A final word about PATA vs SATA There is a lot of advertising out there drives: If you compare the technical that describes the speed of PATA and STAR Watch - 3 - March/April 2005
SATA hard drives as “ATA-100”, turer with identical performance “ATA-133”, or “ATA-150”. While the specs (7200 RPM, ATA-133). As ATA- numeric portion of the description 133 drives, one would assume that does accurately describe the maxi- the drives will be able to move data mum speed (in megabytes/sec.) of at 133 megabytes/sec. But, in the the data transfer from the cache fine print, the manufacturer states buffer to RAM (see Cache Buffer Size that the maximum sustained data below), it only measures a very small rate is 60 megabytes/sec. When I part of the work that the hard drives run speed tests on the drives, one does. The drive must retrieve data computer had a sustained data rate physically from the disk and place it of 29 – 31 megabytes/sec. The other into the cache buffer, or write the achieved 49 – 50 megabytes/sec. data found in the cache buffer onto The computer with the “slower” re- the disk. The sults is a ATA speed meas- 1.3GHz Pentium urement never 4 with 256 MB considers the RAM. The com- most time- puter with the consuming part “faster” hard of the job. drive has a 3.4 GHz 64-bit proc- The true meas- essor with 1 GB urement of overall of RAM. drive performance is “maximum Real world per- sustainable data rate”. This meas- formance is greatly affected by the urement describes the average num- rest of the computer hardware. ber of megabytes of data that the Don’t obsess over the “ATA” speed. drive can move from disk to RAM or Even though the manufacturers move from RAM to disk over an ex- make a big deal about it, it doesn’t tended period of time. Manufactur- have that much affect on real world ers will quote a number that does not performance. take into consideration processor performance or CPU load caused by Rotational Speed applications, which can greatly affect the actual performance of the drive Faster is better. Faster will make a in the real world. Real world results noticeable difference. As the RPMs may be quite different. on a hard drive increase, the time re- quired to move the desired data un- At home, I have two computers. In der the read/write head decreases. each of those computers, are PATA Once located, faster RPMs mean hard drives from the same manufac- faster physical reads and writes of STAR Watch - 4 - March/April 2005 data. Most hard drives sold for use written to disk. That brings up an in desktop computers today are 7200 issue: As the computer gets busier, RPM. This is a significant improve- more and more data requests must ment over the 5400 RPM drives that be processed. It becomes more and were the standard a few years ago. more of a problem to stream the That increase in speed translates data to/from the computer applica- into a 25% reduction in the time re- tion to the disk in a single seamless quired to physically access data. The operation. The cache buffer on the 5400 RPM hard drives are still avail- hard drive allows the process of able for what might seem like a fan- transferring data to/from the hard tastic price, but the reality is that drive to occur in 2 distinct steps, their lack of performance more than which reduces the number of issues negates the price advantage. that must be controlled at any point in time. While there are also hard drives that spin at Bigger is better and be- 10,000 and 15,000 RPM, comes more important most are SCSI, only a as the speed of the proc- few 10K drives are essor increases. The SATA, and none are greater the cache buffer PATA. There are very size, the greater the pos- few SCSI drives spinning sibility that the drive has at 10K or 15K with at a place to put data after capacity greater than retrieving it from disk or 147 Gigabytes. Cur- that it has data that can rently, the largest capac- be written to disk. Most ity 10K SATA drive is 74 Gigabytes. hard drives sold today have an 8 These drives are mostly intended for megabyte disk cache. While it is use in file servers where the de- still possible to find some drives mands can justify the additional with a 2 megabyte cache for a lower cost. For desktop computers, stick price, the loss in performance would with 7200 RPM drives. negate any cost savings.
Cache Buffer Size One vendor, Maxtor, has increased the cache buffer size on some of its Once the data has been physically drives to 16 megabytes. Depending retrieved from the hard disk, it must on the disk I/O load caused by the be moved to a location where the ap- applications running on the com- plication program can use it. Con- puter, disk performance could be versely, if an application is writing improved. It definitely wouldn’t data, it must be moved to a location slow it down. where it will be ready to be physically STAR Watch - 5 - March/April 2005
Native Command Queuing (NCQ)
One of the most innovative features in this new offering of hard drives is Na- tive Command Queuing. Without NCQ, hard drives process requests in the exact order that they were requested. With NCQ, requests are handled in an order that is most efficient for the hard drive. This could increase hard drive performance in peak load situations, which could speed up applications run- ning on the computer.
So how does it work? Consider the following situation: The hard drive has re- ceived commands to read data alternately from the inner then outer portions of the disk. Without NCQ, the drive would dutifully read, then move the heads to the far side of the disk, read a record, move all the way back, etc. The read/write heads are spending a great deal of time moving back and forth to get to the next record. With NCQ invoked, the drive would complete all of the reads in the general location where the read/write heads currently are sta- tioned, then move to the far side of the disk and do the rest of the reads. In this example, the read/write heads would only travel across the disk once. That translates into major time savings. All of the reads got done in much less time.
As of today, only drives manufactured by Maxtor and Seagate have this fea- ture. It should not be long for other vendors to follow.
Summary
Choosing the right hard drive for that new computer or to upgrade an existing computer requires some thought, but isn’t that difficult when you have a rea- sonable understanding of the major issues. The table below provides a quick overview of the information in this article
Cache Cost Max Type RPMs Buffer $/GB Size (GB) PATA 7200 8 or 16 .50 - .75 400 SATA 7200 8 or 16 .50 - .75 400 SATA 10K 8 2.50 – 3.50 74 SCSI 7200 8 or16 3.00 – 3.50 181 SCSI 10K, 15K 8 2.50 – 3.50 300
STAR Watch - 6 - March/April 2005
WNYLC Web Statistics For March 2005
Total Hits………………………….396,058 Accessed Using Internet Explorer.……89% Total User Sessions………………...50,132 Accessed Using Netscape………...…….6% Average Hits/Day Operating Systems Used: (Monday – Friday)………….16,069 Windows 98…………..………..16% Average user Sessions/Weekday…...1,893 Windows 2000……….....……..19% Number of Pages Viewed………….135,729 Windows XP…………...……...52% Average Number of Pages Windows 95……………...... ….<1% Viewed Per Day………..…….4,378 Windows ME…………….....…..1% Number of Documents Viewed…….83,580 Windows NT……………….…...1% Macintosh…………………..….<1% Linux/Unix…………….……...<1%
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