I think during the installation i have to setup the software raid 1 drives. Is this correct?
yes, but no idea how, I find the GUI tools confusing
Is it possible to spin down a raid 5 array? I want save energy overnight when it is not used. I think /var/hda/files will be on the raid 5 array.
yes it is. You will need to modify (or create) /etc/hdparm.conf and add an entry for each disk you want this setting to be active on.
A possible setting is:
Code: Select all
/dev/disk/by-id/scsi-SATA_<brandname>_<type> {
spindown_time = 242
}
example:
/dev/disk/by-id/scsi-SATA_SAMSUNG_HD103UJS13PJDWQC43207 {
spindown_time = 242
}
/dev/disk/by-id/scsi-SATA_SAMSUNG_HD753LJS13UJDWQ828015 {
spindown_time = 242
}The above setting will spin down your disks after 1 hour. The calculation rules are quite esoteric, but they are explained in the
hdparm manpage.
small excerpt from that manpage:
-S
Set the standby (spindown) timeout for the drive. This value is used by the drive to determine how long to wait (with no disk activity) before turning off the spindle motor to save power. Under such circumstances, the drive may take as long as 30 seconds to respond to a subsequent disk access, though most drives are much quicker. The encoding of the timeout value is somewhat peculiar. A value of zero means "timeouts are disabled": the device will not automatically enter standby mode. Values from 1 to 240 specify multiples of 5 seconds, yielding timeouts from 5 seconds to 20 minutes. Values from 241 to 251 specify from 1 to 11 units of 30 minutes, yielding timeouts from 30 minutes to 5.5 hours. A value of 252 signifies a timeout of 21 minutes. A value of 253 sets a vendor-defined timeout period between 8 and 12 hours, and the value 254 is reserved. 255 is interpreted as 21 minutes plus 15 seconds. Note that some older drives may have very different interpretations of these values.
Note however that with spinning down the array when not used will yield a significantly longer seek time the first time the disks are accessed again. Furthermore you will
increase the wear and tear of the drives to save an almost insignificant amount of power.
Five drives running without actively seeking would likely use about 2 Watts each, if they are late-generation ones. That means you'd conserve around 10W per hour for your complete RAID array in the best case scenario.
So what does that tell us? Let me calculate the cost savings
10Wh * 12h = 0,12KWh per day on weekdays
10Wh * 24h = 0,24KWh per day on weekends
(5d * 0,12KWh) + (2d * 0,24KWh) = 1,08KWh per week
You're Dutch, so you'll likely pay around € 0,085 per KWh (8.5 cents) on a fixed tariff
(52w * 1,08KWh) * € 0,085 = € 4,77 (rounded up) per year.
- if you have "Piek & Dal" tariff you'll pay around 0,10 cents during the daytime in which the server is used and 6,5 cents in which the server is not used so you'd save (52w * 1,08KWh) * € 0,065 = € 3,65
I
can try to factor in the costs for the wear and tear but that would be highly speculative so I won't go into detail. Let's just state that the drives will last 3 years until you need to replace them. Over the 3 years you'd conserve a little more than 3KWh and the cost savings would be beteen € 12,-- and € 15,-- (including a little price inflation).
It's your decision if that's worth the effort
When in the future mail is supported is should be nice if this mail software is running on the Server OS drive (raid 1). The raid 1 drives are always spinning and you can save energy overnight to spin down the raid 5 array.
Typically mail is processed in /var/spool/mail (unless specified differently) so it would be on the RAID1 array anyway.
Hope this answers your questions
) as well. Not sure if it helps, but hey...