[sclug] Newbie, partitioning 120Gb HDD - recommendations?

[Alex Butcher]

On Tue, 18 Jan 2005, Tom Dawes-Gamble wrote:

> On Tue, 2005-01-18 at 11:50 +0000, Alex Butcher wrote:
>
>> I agree, modulo the decreasing transfer rate from rotational discs as you
>> get closer to the hub (the usual virtual->phsyical mapping used by hard
>> discs, though this is not guaranteed). In general, putting active partitions
>> (e.g. /tmp, /var/cache, /home, /usr) near the beginning of the disc gives
>> better performance than putting them at the end (a good place for
>> /var/spool, though).
>>
>
> I'm not sure about this idea that it's faster to put things near the
> centre or the perimeter.  If the track at the centre has the same number
> of sectors as the track at the outside then the packing density is
> greater in the centre  *BUT* it takes the same time for the outer
> sectors to pass under the head as it does for the inner sectors.

*Modern* discs *don't* have the same number of physical sectors on outer
tracks as inner tracks, hence:

# fdisk -l /dev/hde

Disk /dev/hde: 200.0 GB, 200049647616 bytes
255 heads, 63 sectors/track, 24321 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

    Device Boot      Start         End      Blocks   Id  System
/dev/hde1               1         499     4008186    c  W95 FAT32 (LBA)
/dev/hde2   *         500         761     2104515   83  Linux
/dev/hde3             762        1023     2104515   83  Linux
/dev/hde4            1024       24321   187141185    f  W95 Ext'd (LBA)
/dev/hde5            1024        3016    16008741    c  W95 FAT32 (LBA)
/dev/hde6            3017        5009    16008741   83  Linux
/dev/hde7            5010        8994    32009481   fd  Linux raid
autodetect
/dev/hde8            8995        9238     1959898+  82  Linux swap
/dev/hde9            9239       24321   121154166   fd  Linux raid
autodetect
# hdparm -tT /dev/hde1

/dev/hde1:
  Timing cached reads:   1940 MB in  2.00 seconds = 969.18 MB/sec
  Timing buffered disk reads:  150 MB in  3.03 seconds =  49.58 MB/sec
[root at caffeine ~]# hdparm -tT /dev/hde1

/dev/hde1:
  Timing cached reads:   1944 MB in  2.00 seconds = 971.66 MB/sec
  Timing buffered disk reads:  144 MB in  3.03 seconds =  47.59 MB/sec
# hdparm -tT /dev/hde9

/dev/hde9:
  Timing cached reads:   1956 MB in  2.00 seconds = 977.66 MB/sec
  Timing buffered disk reads:  102 MB in  3.03 seconds =  33.68 MB/sec
# hdparm -tT /dev/hde9

/dev/hde9:
  Timing cached reads:   1960 MB in  2.00 seconds = 978.68 MB/sec
  Timing buffered disk reads:  104 MB in  3.09 seconds =  33.66 MB/sec

That disc is a recent Seagate ST3200822A 200GByte PATA model.
<http://www.pcguide.com/ref/hdd/geom/tracksZBR-c.html> shows a 9 year old
Quantum Fireball disc as having 14 zones, ranging from 232 sectors/track
down to 122 sectors/track with corresponding transfer rates dropping from
92.9Mbits/s at the rim zone to 49.5Mbits/s at the hub zone. A newer 5 year
old IBM disc also has 14 zones, ranging from 792 spt/372Mbits/s to 370
spt/172.8Mbits/s.

Note that the cached reads remain constant at ~970MByte/s, but buffered disk
reads are ~40% slower by the 40% mark of the disc (I suspect the 40% values
as being coincidental, rather than directly proportional, otherwise one
would expect 100% slower at the 100% mark!).

> Tom.

Best Regards,
Alex.
-- 
Alex Butcher      Brainbench MVP for Internet Security: www.brainbench.com
Bristol, UK                      Need reliable and secure network systems?
PGP/GnuPG ID:0x271fd950                         <http://www.assursys.com/>