WD Green Discs and the problem in Linux (Load Cycle Count)

While many people report that WD Green Discs are “bad” i wouldn’t say so. I’d say they’re the best SATA drives I’ve ever had – even with the problematic load-cycle-count. But let’s take a closer look at these discs.

The WD Green drives used in this article are: WDC WD5000AADS. These drives got 500 GB and 32 MB cache, hdparm reports that they have a read speed of 100 MB/s (hdparm -tT –direct!) and with SW Raid 5 over 4 discs I’m able to write at ~220 MB/s and read at 275 MB/s (so the discs aren’t bad), the sound is also fine – i cannot hear the discs, the cache is awesome. Warning: I’m not responsible for any damage YOU are doing to YOUR hardware by using software or things I wrote about here. YOU’RE doing everything on YOUR OWN Risk.

However, back to the Problem. Linux per default wakes discs up every 5 seconds. Some distributions and tools like powertop suggest to increase this value to 15.

Quote from /usr/src/linux/Documentation/sysctl/vm.txt

dirty_writeback_centisecs

The pdflush writeback daemons will periodically wake up and write `old' data
out to disk.  This tunable expresses the interval between those wakeups, in
100'ths of a second.

Setting this to zero disables periodic writeback altogether.

The default value is

cat /proc/sys/vm/dirty_writeback_centisecs
500

Which is 5 seconds. To increase it you’d do:

echo 1500 > /proc/sys/vm/dirty_writeback_centisecs

Which’d be 15 seconds. I wouldn’t suggest you to increase it even further. I’m using 5 minutes, though:

1500=15 | x4
6000=60 | x5
30000=300

But that’s just one part of the problem. See, the filesystem itself is syncing data all 5 seconds thus waking the discs up.

Quote from man mount

       commit=nrsec
              Sync  all  data  and  metadata  every nrsec seconds. The default
              value is 5 seconds. Zero means default.

So while we just managed to stop the periodic wake up of our harddisc, it’s still waking the discs up every 5 seconds because of the syncing (filesystem). I changed that value to 300, too.

However – I bought these discs because they’re power-saving. So i also want to take advantage of that. What I’m doing is simple, I’m setting my discs to standby after 1 minute (this causes a spin down, disc’ll stay in standby for at least 4 minutes with the above settings. Changing between standby and active/idle doesn’t seem to change the Load_Cycle_Count. Don’t use the “sleep” feature – like

hdparm -Y

because this will increase the load_cycle_count. So proper setting would be something like

hdparm -S 12 /dev/sdb

to put the disc into standby after 1 minute idle. According to some specs i found the disc takes

  • 5.4 Watt while reading/writing
  • 2,5 Watt in idle
  • 0.46 Watt in standby
  • 0.46 Watt in sleep

So i guess putting it only into standby is enough. However, the real questions are:

Is a disc corrupt or at It’s end life time when a load cycle count is reached which is higher than the supported one?

You should contact WD and ask them about it – However, from what i can tell you, my discs reached a bit more and they’re still running very fine:

sdb
193 Load_Cycle_Count        0x0032   056   056   000    Old_age   Always       -       434974
  9 Power_On_Hours          0x0032   090   090   000    Old_age   Always       -       7548
= 314 days

sdc
193 Load_Cycle_Count        0x0032   056   056   000    Old_age   Always       -       434837
  9 Power_On_Hours          0x0032   090   090   000    Old_age   Always       -       7550
= 314 days

sdd
193 Load_Cycle_Count        0x0032   058   058   000    Old_age   Always       -       426896
  9 Power_On_Hours          0x0032   090   090   000    Old_age   Always       -       7554
= 314 days

sde
193 Load_Cycle_Count        0x0032   192   192   000    Old_age   Always       -       26046
  9 Power_On_Hours          0x0032   100   100   000    Old_age   Always       -       373
= 6 days

The last disc is brand new as you can see.

Is it the discs fault or Linux’ fault?

Heh. This one isn’t easy to answer, just check your netbook/notebook. Most likely the discs in your netbook/notebook will have similar values, because those discs are made for that. Discs for notebooks were always made for the “best” power-saving possible – So you can do aggressive power saving with them (or they’re doing that by themself) without trashing them. These WD discs are in short just doing the same, and I’m sure (of course i don’t know) they’re exactly made for that – So saying it’s WD’s fault or the discs are crap is just dumb in my humble opinion. The discs are fine and they’re doing what they should. HOWEVER: the low delays of linux on the contrary are bad. Of course if you increase them the following happens: You’re downloading something, now you’re pressing reset (hard reset / power down without waiting for the filesystem to sync) and the file you just downloaded is corrupt or gone. However, you should always reboot or power down correctly. If you power-off your system correctly, the init scripts will sync the filesystems, and thus the harddiscs, properly BEFORE they’re shut down – Thus you won’t lose data. So everything which wasn’t written yet, gets written as soon as the data is synced (for example by init script when doing umount) – So you would lose data ONLY in case of a power-outage. The settings of “sync every 5 seconds” are useful if you’re running critical stuff and in case of a power-outage you got the most of your data still around. So again: Is it Linux’ fault? No. Because it tries to save you from data loss. It’s up to you, to find a trade off between security and energy-saving.

So, how can i disable this head-parking

BIG FAT WARNING: If you’re doing this, or using the tool, i take no warranty for any damage which might occur. You’re doing it on your own risk.

There’s a tool from WD called wdidle, there are also some freedos images with it so you can disable it quite fine. Some months ago i wrote a little post in a related board, you can read my post here. In the same board you should find additional information about wdidle so just keep reading there. Boot from a freedos cd with wdidle on it and type in wdidle3.exe – It’ll display the current settings. To disable it i had to do wdidle3.exe \D, be careful, some people reported that might make it worse on some specific discs.

One little hint: I had to set my controller to IDE Mode (just for the DOS stuff, you can change it back later) to have that working. So if you got a mainboard where you can choose between IDE Mode, AHCI Mode and RAID mode you might want to change to IDE mode – Otherwise wdidle doesn’t detect my discs here.

Conclusion?

I’ll still buy WD discs – I do that since years and I won’t stop it.

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  2. wd caviar green load cycle count » trivia

    […] trouble with a RAID 5 setup and had discovered that others with the same problem were also using WD Green drives. These drives park the heads rather aggressively as part of the power saving features, […]

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