Thank you for purchasing through links and ads on this site.
OWC / MacSales.com...
diglloyd Deal Finder...
Buy other stuff at Amazon.com...
Get up to 16x more storage and 2x the speeds of the original drive
Handpicked deals...
$1799 $1399
SAVE $400

$719 $230
SAVE $489

$198 $138
SAVE $60

$695 $195
SAVE $500

$1997 $897
SAVE $1100

$1099 $999
SAVE $100

$348 $278
SAVE $70

$348 $278
SAVE $70

$3099 $2499
SAVE $600

$2099 $1799
SAVE $300

$275 $275
SAVE $0

$699 $499
SAVE $200

$1699 $1299
SAVE $400

$2999 $2999
SAVE $0

$1699 $1443
SAVE $256

$2798 $2498
SAVE $300

$2399 $2249
SAVE $150

$3798 $1898
SAVE $1900

$2798 $2498
SAVE $300

$2497 $1997
SAVE $500

$2498 $1798
SAVE $700

$3297 $2197
SAVE $1100

$2798 $2498
SAVE $300

$2998 $2498
SAVE $500

$1398 $1198
SAVE $200

$898 $798
SAVE $100

$400 $250
SAVE $150

$1299 $939
SAVE $360

$4078 $4078
SAVE $0

$4499 $2999
SAVE $1500

$4999 $4599
SAVE $400

$2199 $1999
SAVE $200

$2799 $2349
SAVE $450

$3099 $2499
SAVE $600

$2001 $1298
SAVE $703

$249 $149
SAVE $100

$2844 $2297
SAVE $547

$1199 $1099
SAVE $100

$2019 $1399
SAVE $620

$999 $949
SAVE $50

Why you should avoid Port Multiplication

Last updated 2009-06-01 - Send Feedback
Related: eSATA, hard drive, optimization, storage

Port multiplication (PM) technology shares a single 3-gigabit SATA cable to connect multiple hard drives, typically up to five.

Unfortunately, as few as two of today’s fast hard drives can saturate the bandwidth of that single cable! Performance is limited to the ~240MB/sec range, even though five drives might be capable of 600MB/sec or more of sustained data transfer. All PM enclosures top out at around 200-230MB/sec, regardless of the number of drives. That’s because they send all data over a single eSATA cable.

Port multiplication technology is perfectly fine if 240MB/sec is all the performance you require and/or your main goal is to create a very large volume by striping multiple hard drives.

You can work around the limitations of port multiplication by using two or three port-multiplied enclosures, each with its own cable. But unless you need a huge amount of storage it’s rather silly: you might as well choose a single non-PM enclosure with 2 or 4 drive bays (see Recommended Hardware page).

There is the argument that PM enclosures provide “even performance across the drive”. In actual fact, PM reduces performance everywhere by throttling performance to half-speed or worse. One can just as well partition drive(s) and maintain high performance across a desired capacity.

The green/blue lines below show that the claim for consistent performance doesn’t entirely hold up under scrutiny: observe the 0% mark. Results obtained with DiskTester.

Performance penalty using Port Multiplication
Horizontal axis represents % across the drive, vertical is MB/sec
(4-drive stripe using Western Digital 1TB RE3)

The graph above shows the huge performance hit from port multiplication. Striped RAID performance with as few as two fast drives will suffer from a port-multiplied enclosure. Your choice for really fast eSATA is to use two or more PM enclosures, or to use a non-PM enclosure, the latter always providing superior performance with the same number of drives.

Always test your setup with DiskTester.


MacPerformanceGuide.com
View all handpicked deals...

Dell UltraSharp 27 U2717D 27" 16:9 InfinityEdge IPS Monitor
$719 $230
SAVE $489

diglloyd.com | Terms of Use | PRIVACY POLICY
Contact | About Lloyd Chambers | Consulting | Photo Tours
Mailing Lists | RSS Feeds | Twitter
Copyright © 2019 diglloyd Inc, all rights reserved.
Display info: __RETINA_INFO_STATUS__