On 5/13/2013 7:10 PM, S H wrote:
My disk is utilized by many other components, thus do we have minimum
recommendation my postgres to have sufficient speed. Current
perfomance of my disk is around 1-5MB/sec. Is it sufficient?
how are you measuring this? thats painfully slow by today's standards,
even my desktop SATA drives can sustain well over 100MB/second on
sequential read or write
what counts in a database server like postgres is NOT the sequential
transfer speed, instead its the random IO operations/second. I'm
benchmarking a 8 disk RAID10 right now and seeing around 2000-4000
write/sec and as high as 1000-2400 read/sec during this TPC-B style
transaction benchmark. iostat -xm during this operation looks like...
avg-cpu: %user %nice %system %iowait %steal %idle
3.34 0.00 1.93 39.43 0.00 55.31
Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz
avgqu-sz await svctm %util
sdb 0.00 0.10 153.50 4901.30 1.89 40.69
17.25 211.50 42.57 0.20 100.00
avg-cpu: %user %nice %system %iowait %steal %idle
10.95 0.00 3.98 36.35 0.00 48.72
Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz
avgqu-sz await svctm %util
sdb 0.00 0.10 583.40 2955.40 7.10 28.75
20.75 215.77 63.01 0.28 99.97
avg-cpu: %user %nice %system %iowait %steal %idle
44.36 0.00 14.28 24.61 0.00 16.75
Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz
avgqu-sz await svctm %util
sdb 0.00 1.10 2377.30 1062.90 29.23 29.97
35.24 29.53 8.59 0.29 99.95
avg-cpu: %user %nice %system %iowait %steal %idle
48.39 0.00 16.45 21.18 0.00 13.98
Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz
avgqu-sz await svctm %util
sdb 0.00 0.00 2564.30 1182.40 31.15 32.42
34.75 28.81 7.69 0.27 99.97
avg-cpu: %user %nice %system %iowait %steal %idle
44.59 0.00 15.02 25.38 0.00 15.02
Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz
avgqu-sz await svctm %util
sdb 0.00 0.10 2346.10 1097.50 28.66 29.28
34.46 29.58 8.60 0.29 99.98
(these are 10 second averages)
in general, the solution to more storage performance for a database
server is to use more disks in a raid10 configuration, I have some
raids that are a many as 20 disks, dedicated to database use (everything
else on the server uses other storage). These are all 15000rpm SAS2
server drives, on a raid controller with 1GB flash-backed write-back cache.
--
john r pierce 37N 122W
somewhere on the middle of the left coast
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