Thank you for purchasing through links and ads on this site.
OWC / MacSales.com...
diglloyd Deal Finder...
Buy other stuff at Amazon.com...
Upgrade the memory of your 2018 Mac mini up to 64GB
Handpicked deals...
$390 $270
SAVE $120

$1798 $1598
SAVE $200

$3297 $2797
SAVE $500

$3397 $2797
SAVE $600

$150 $90
SAVE $60

$1398 $898
SAVE $500

$3698 $2998
SAVE $700

$2998 $2498
SAVE $500

$1799 $1299
SAVE $500

$1999 $1199
SAVE $800

$2299 $1599
SAVE $700

$2399 $2049
SAVE $350

$2799 $2399
SAVE $400

$2799 $1899
SAVE $900

$1199 $920
SAVE $279

$1349 $1049
SAVE $300

$997 $897
SAVE $100

$2099 $1699
SAVE $400

$1999 $1349
SAVE $650

$1999 $1599
SAVE $400

$1999 $1999
SAVE $0

$1329 $929
SAVE $400

$4499 $3999
SAVE $500

$329 $329
SAVE $0

$1499 $999
SAVE $500

$1499 $1289
SAVE $210

$2199 $1999
SAVE $200

$3399 $2199
SAVE $1200

$2468 $1768
SAVE $700

Speed: RAID 1 Mirroring

See About RAID-1 Mirroring.

For reads with a RAID-1 mirror there is potential to distribute reads across more than one drive, since all drives contain the same data, thus enhancing read performance. However, read speed is never as as good as RAID-0 striping because the reads are offset (staggered) among the drive members of the mirror, but an optimized controller or driver can extract some benefits.

Typical RAID-1 mirror 2-drive setups with hard drives show little or no benefit from reading from multiple drives, whether the mirror is hardware of software based. A three drive setup offers more potential for improvement.

With SSDs (flash drives), the potential for speeds is far higher, since SSDs do not have the latency issues of hard drives.

Reads matter more than writes for most uses

Raw image files, video, music and similar all get written once and rarely if ever change. Since most user activity is read-based (not writes), an increase in read speed is a meaningful advantage of using a three-drive RAID-1 mirror.

Moreover, write-speed optimization using hard drives is often a losing game anyway: far better to use a fast SSD when write performance is a significant issue.

As a bonus, using three drives in a mirror yields substantially more fault tolerance as well (versus two drives).

Test results

Tested with three fast Toshiba 7200 rpm DT01ACAxx series drives using SoftRAID 5 with “Use all disks for mirror reads” enabled.

This graph using the CalDigit T3 , which has ample bandwidth for this test.

MB/sec:
Single drive: 184 write / 181 read
2-drive mirror: 184 write / 198 read
3-drive mirror: 184 write / 271 read

A 2-drive mirror offers brief spikes of better performance than a single drive averaging 9% faster than a single drive—not nothing but not much either.

A 3-drive mirror delivers about 50% higher read speed than that of a single drive.

Write speeds are in gray and are the same it is a single drive or a 2-drive or 3-drive mirror—this is as expected.

CalDigit T3 Thunderbolt: RAID-1 mirror speed (2 and 3 drives) vs single drive

An example with slower drives

Drive speed and latency can limit the benefits. In the test below, the slower 4TB Hitachi 7K4000 drives were used. Four drives are a little faster than three as shown, but no faster than a 3-drive mirror of the Toshiba drives in the graph shown above.

MB/sec:
Single drive: 162 write / 158 read
2-drive mirror: 159 write / 173 read
3-drive mirror: 158 write / 239 read
4-drive mirror: 158 write / 271 read

CalDigit T3 Thunderbolt: RAID-1 mirror speed (2 and 3 drives) vs single drive

An example with SSD

Solids state (flash) drives don’t have the latency issues of hard drives.

Here, with two mistmatched SSDs, the mirrored read speed has hit 787 MB/sec, which exceeds what Promise Technology states is the speed for the Pegasus J4 (“Delivers over 750MB/s with SSDs”). A 4-drive SSD stripe maxes out at less than 900MB/sec, so seeing 787MB/sec with two mismatched SSDs is rather good.

CalDigit T3 Thunderbolt: RAID-1 mirror speed with two mistmatched SSDs

 

Apple 13-inch MacBook Pro
Only $1799 $1149

8GB / 256GB SSD / 2.3 Ghz Intel Core i5

Apple Refurbished Factory Sealed
Apple 1 Year Limited Warranty
Awesome for a student!
Apple iMac 5K Speed Demon
$3849
$3499

It rocks! What Lloyd uses every day, best upgrade in many years!

SMART MOVES:
• Add 128GB or 64GB memory
fast SSD storage
Thunderbolt storage

√ B&H Photo PAYS THE SALES TAX FOR YOU More info...

Save the tax, we pay you back, instantly!
View all handpicked deals...

Samsung 2TB T5 Portable Solid-State Drive (Black)
$390 $270
SAVE $120

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__