Have many disks. More disk spindles brings more than capacity alone! (Same as in databases)

Speed

Slow laptop 2.5" 5400 disk

dpavlin@llin:~$ sudo hdparm -i /dev/sda

/dev/sda:

 Model=FUJITSU MHV2080BH                       , FwRev=00840028, SerialNo=        NW05T6B29HM5
 Config={ HardSect NotMFM HdSw>15uSec Fixed DTR>10Mbs }
 RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=4
 BuffType=DualPortCache, BuffSize=8192kB, MaxMultSect=16, MultSect=?16?
 CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=156301488
 IORDY=on/off, tPIO={min:240,w/IORDY:120}, tDMA={min:120,rec:120}
 PIO modes:  pio0 pio1 pio2 pio3 pio4 
 DMA modes:  mdma0 mdma1 mdma2 
 UDMA modes: udma0 udma1 udma2 udma3 udma4 *udma5 
 AdvancedPM=yes: mode=0x80 (128) WriteCache=enabled
 Drive conforms to: unknown:  ATA/ATAPI-3,4,5,6,7

 * signifies the current active mode

dpavlin@llin:~$ sudo hdparm -tT /dev/sda
/dev/sda:
 Timing cached reads:   1566 MB in  2.00 seconds = 782.85 MB/sec
 Timing buffered disk reads:   66 MB in  3.03 seconds =  21.79 MB/sec

Faster (!) external 3.5 USB disk (no hdparm -i on USB), but just because it's another disk not loaded by system.

dpavlin@llin:~$ sudo hdparm -tT /dev/sdb

/dev/sdb:
 Timing cached reads:   1508 MB in  2.00 seconds = 753.72 MB/sec
 Timing buffered disk reads:   56 MB in  3.03 seconds =  18.48 MB/sec

Home-made software md RAID 5 array from SATA drives:

dpavlin@brr:~$ sudo hdparm -i /dev/sdd

/dev/sdd:

 Model=WDC WD5000AAKS-00YGA0                   , FwRev=12.01C02, SerialNo=     WD-WCAS80929678
 Config={ HardSect NotMFM HdSw>15uSec SpinMotCtl Fixed DTR>5Mbs FmtGapReq }
 RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=50
 BuffType=unknown, BuffSize=16384kB, MaxMultSect=16, MultSect=?16?
 CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=976773168
 IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120}
 PIO modes:  pio0 pio3 pio4 
 DMA modes:  mdma0 mdma1 mdma2 
 UDMA modes: udma0 udma1 udma2 udma3 udma4 udma5 *udma6 
 AdvancedPM=no WriteCache=enabled
 Drive conforms to: Unspecified:  ATA/ATAPI-1,2,3,4,5,6,7

 * signifies the current active mode

dpavlin@brr:~$ sudo hdparm -tT /dev/sda /dev/sdb /dev/sdd

/dev/sda:
 Timing cached reads:   1982 MB in  2.00 seconds = 991.18 MB/sec
 Timing buffered disk reads:  232 MB in  3.03 seconds =  76.67 MB/sec

/dev/sdb:
 Timing cached reads:   2010 MB in  2.00 seconds = 1004.95 MB/sec
 Timing buffered disk reads:  228 MB in  3.01 seconds =  75.85 MB/sec

/dev/sdd:
 Timing cached reads:   2006 MB in  2.00 seconds = 1003.01 MB/sec
 Timing buffered disk reads:  230 MB in  3.01 seconds =  76.47 MB/sec

dpavlin@brr:~$ cat /proc/mdstat 
Personalities : [raid6] [raid5] [raid4] 
md0 : active raid5 sdd1[0] sda1[2] sdb1[1]
      976767872 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU]

dpavlin@brr:~$ sudo hdparm -tT /dev/md0

/dev/md0:
 Timing cached reads:   1986 MB in  2.00 seconds = 993.20 MB/sec
 Timing buffered disk reads:  434 MB in  3.01 seconds = 144.41 MB/sec

As expected RAID 5 speed is 75 + 75 + 0 (parity disk) ~ 144 MB/sec

temperature

root@brr:~# hddtemp /dev/sda /dev/sdb /dev/sdd
/dev/sda: WDC WD5000AAKS-00YGA0: 33°C
/dev/sdb: WDC WD5000AAKS-00YGA0: 32°C
/dev/sdd: WDC WD5000AAKS-00YGA0: 32°C

Data security

Smart

root@brr:~# smartctl --all /dev/sda | head -20
smartctl version 5.38 [i686-pc-linux-gnu] Copyright (C) 2002-8 Bruce Allen
Home page is http://smartmontools.sourceforge.net/

=== START OF INFORMATION SECTION ===
Model Family:     Western Digital Caviar Second Generation Serial ATA family
Device Model:     WDC WD5000AAKS-00YGA0
Serial Number:    WD-WCAS80815866
Firmware Version: 12.01C02
User Capacity:    500,107,862,016 bytes
Device is:        In smartctl database [for details use: -P show]
ATA Version is:   8
ATA Standard is:  Exact ATA specification draft version not indicated
Local Time is:    Sat Oct 11 00:27:01 2008 CEST
SMART support is: Available - device has SMART capability.
SMART support is: Enabled

=== START OF READ SMART DATA SECTION ===
SMART overall-health self-assessment test result: PASSED

Before you start to beleve in SMART as solution to all disk health problems, read Failure Trends in a Large Disk Drive Population

RAID

Also interesting is Some RAID Issues