Harddrive Write Cache Disabled.

[joshuah]

Don't need to wait for synology, I can tell you right now. YES there will be a performance impact. How big of impact? Depends on your IO profile. Read cache is less important than write cache, because to read something you have to get it from the spindel, so you are bound to the medium anyway. On a contrary, a write to the harddrive doesn't mean that data has to be written immediately on the spindle, it can be written to the cache... and then when the hard drive head passes over ( fly by ) an area where data needs to be stored the IO request gets executed, this reduces the hard drive head movement significantly and the stress on the mechanics.
This is the theory and the work on high end storage, don't know if it's the same for SATA hard drives and low end systems.

[microkid]

Looking in /usr/syno/etc.defaults/scemd.xml it appears they added some code to disable write cache on specific drive models. So this appears to be a feature and not a bug.

Code: Select all

<disk_control>
   <disk model="ST9120821A">APM_255</disk>
   <disk model="HTS722020K9SA00">APM_255</disk>
   <disk model="ST980811AS">APM_255</disk>
   <disk model="MHV2060BH">APM_255</disk>
   <disk model="MK6034GSX">APM_254</disk>
   <disk model="ST9100824AS">APM_255</disk>
   <disk model="HM250JI">APM_255</disk>
   <disk model="MK1637GSX">APM_254</disk>
   <disk model="ST9100824AS">APM_255</disk>
   <disk model="ST9120822AS">APM_254</disk>
   <disk model="ST9160821AS">APM_254</disk>
   <disk model="WD2500BEVS-75UST0">APM_254</disk>
   <disk model="HM250JI">APM_254</disk>
   <disk model="WD2500BEVS">APM_254</disk>
   <disk model="WD1600BEVT">APM_255</disk>
   <disk model="HTS543232L9A300">APM_255</disk>
   <disk model="WD1600BEVE">APM_255</disk>
   <disk model="MK2546GSX">APM_254</disk>
   <disk model="MHV2080BHPL">APM_255</disk>
   <disk model="WD1200BEVE">APM_255</disk>
   <disk model="HTS543225L9A300">APM_255</disk>
   <disk model="WD3200BEVT">APM_254</disk>
   <disk model="MK8025GAS">APM_254</disk>
   <disk model="ST9200420AS">APM_254</disk>
   <disk model="WD3200BEVT">APM_254</disk>
   <disk model="HTS543216L9SA00">APM_254</disk>
   <disk model="MK4058GSX">APM_254</disk>
   <disk model="WD6400BEVT">APM_254</disk>
   <disk model="ST32000542AS">APM_255</disk>
   <disk model="ST95005620AS">APM_255</disk>
   <disk model="WD7500BPVT">APM_254</disk>
   <disk model="WD30EZRX">WCACHE_OFF</disk>
   <disk model="WD25EZRX">WCACHE_OFF</disk>
   <disk model="WD20EARX">WCACHE_OFF</disk>
   <disk model="WD15EARX">WCACHE_OFF</disk>
   <disk model="WD10EADX">WCACHE_OFF</disk>
   <disk model="WD7500AARX">WCACHE_OFF</disk>
   <disk model="WD30EZRSDTL">WCACHE_OFF</disk>
   <disk model="WD25EZRSDTL">WCACHE_OFF</disk>
   <disk model="WD20EARS">WCACHE_OFF</disk>
   <disk model="WD15EARS">WCACHE_OFF</disk>
   <disk model="WD10EARS">WCACHE_OFF</disk>
   <disk model="WD8000AARS">WCACHE_OFF</disk>
   <disk model="WD7500AARS">WCACHE_OFF</disk>
   <disk model="WD6400AARS">WCACHE_OFF</disk>
   <disk model="WD20EADS">WCACHE_OFF</disk>
   <disk model="WD15EADS">WCACHE_OFF</disk>
   <disk model="WD10EADS">WCACHE_OFF</disk>
   <disk model="WD8088AADS">WCACHE_OFF</disk>
   <disk model="WD7500AADS">WCACHE_OFF</disk>
   <disk model="WD6400AADS">WCACHE_OFF</disk>
   <disk model="WD5000AADS">WCACHE_OFF</disk>
   <disk model="WD3200AACS">WCACHE_OFF</disk>
   <disk model="ST32000542AS">WCACHE_OFF</disk>
   <disk model="ST31500541AS">WCACHE_OFF</disk>
   <disk model="ST31000520AS">WCACHE_OFF</disk>
   <disk model="ST3500412AS">WCACHE_OFF</disk>
</disk_control>

So, can't we just edit this file and remove the line that contains our particular harddisk type?

[Zouk !]

Looking in /usr/syno/etc.defaults/scemd.xml it appears they added some code to disable write cache on specific drive models. So this appears to be a feature and not a bug.

Code: Select all

<disk_control>
   <disk model="ST9120821A">APM_255</disk>
   <disk model="HTS722020K9SA00">APM_255</disk>
   <disk model="ST980811AS">APM_255</disk>
   <disk model="MHV2060BH">APM_255</disk>
   <disk model="MK6034GSX">APM_254</disk>
   <disk model="ST9100824AS">APM_255</disk>
   <disk model="HM250JI">APM_255</disk>
   <disk model="MK1637GSX">APM_254</disk>
   <disk model="ST9100824AS">APM_255</disk>
   <disk model="ST9120822AS">APM_254</disk>
   <disk model="ST9160821AS">APM_254</disk>
   <disk model="WD2500BEVS-75UST0">APM_254</disk>
   <disk model="HM250JI">APM_254</disk>
   <disk model="WD2500BEVS">APM_254</disk>
   <disk model="WD1600BEVT">APM_255</disk>
   <disk model="HTS543232L9A300">APM_255</disk>
   <disk model="WD1600BEVE">APM_255</disk>
   <disk model="MK2546GSX">APM_254</disk>
   <disk model="MHV2080BHPL">APM_255</disk>
   <disk model="WD1200BEVE">APM_255</disk>
   <disk model="HTS543225L9A300">APM_255</disk>
   <disk model="WD3200BEVT">APM_254</disk>
   <disk model="MK8025GAS">APM_254</disk>
   <disk model="ST9200420AS">APM_254</disk>
   <disk model="WD3200BEVT">APM_254</disk>
   <disk model="HTS543216L9SA00">APM_254</disk>
   <disk model="MK4058GSX">APM_254</disk>
   <disk model="WD6400BEVT">APM_254</disk>
   <disk model="ST32000542AS">APM_255</disk>
   <disk model="ST95005620AS">APM_255</disk>
   <disk model="WD7500BPVT">APM_254</disk>
   <disk model="WD30EZRX">WCACHE_OFF</disk>
   <disk model="WD25EZRX">WCACHE_OFF</disk>
   <disk model="WD20EARX">WCACHE_OFF</disk>
   <disk model="WD15EARX">WCACHE_OFF</disk>
   <disk model="WD10EADX">WCACHE_OFF</disk>
   <disk model="WD7500AARX">WCACHE_OFF</disk>
   <disk model="WD30EZRSDTL">WCACHE_OFF</disk>
   <disk model="WD25EZRSDTL">WCACHE_OFF</disk>
   <disk model="WD20EARS">WCACHE_OFF</disk>
   <disk model="WD15EARS">WCACHE_OFF</disk>
   <disk model="WD10EARS">WCACHE_OFF</disk>
   <disk model="WD8000AARS">WCACHE_OFF</disk>
   <disk model="WD7500AARS">WCACHE_OFF</disk>
   <disk model="WD6400AARS">WCACHE_OFF</disk>
   <disk model="WD20EADS">WCACHE_OFF</disk>
   <disk model="WD15EADS">WCACHE_OFF</disk>
   <disk model="WD10EADS">WCACHE_OFF</disk>
   <disk model="WD8088AADS">WCACHE_OFF</disk>
   <disk model="WD7500AADS">WCACHE_OFF</disk>
   <disk model="WD6400AADS">WCACHE_OFF</disk>
   <disk model="WD5000AADS">WCACHE_OFF</disk>
   <disk model="WD3200AACS">WCACHE_OFF</disk>
   <disk model="ST32000542AS">WCACHE_OFF</disk>
   <disk model="ST31500541AS">WCACHE_OFF</disk>
   <disk model="ST31000520AS">WCACHE_OFF</disk>
   <disk model="ST3500412AS">WCACHE_OFF</disk>
</disk_control>

So, can't we just edit this file and remove the line that contains our particular harddisk type?

Hi,

I think it will be better to try getting an official statement from Synology about this "choice", I guess if they explicitly turned off cache for a bunch of drive, there probably a (good ?) reason which will be interesting to learn before to change anything (it's only an advice).
On the other hand, personally, I always deactivated write cache since they never activated write barrier when cache was on, although it was on DSM3.x I don't think this behavior has change with DSM4.x (but I didn't checked,), well, it's another story, back to thread.

Best Regards,
Zouk !

[microkid]

Well, it worked fine in 3.2 and I assume the majority of the core programming in 4.0 did not change. So an explanation from Synology would be very welcome indeed. I contacted technical support, now let's see what they can do for us

[Metrik]

We definitely could use an explanation from Synology on this issue.

Before buying my two hard drives for my DS212j, I checked the Synology hard drive compatibility list and SPECIFICALLY PICKED a drive that was fully supported. I also went for a model with a large cache. I feel a bit cheated now. Stupid, even.

[jekyll]

Looks like a change to the Advanced Power Management, Could this be related to LCC?

EDIT: also APM is set at 254 for many drives, could this be related to hibernation?

Found this on my google travels:

The advanced power management appeared as an option in the hard disk drives supporting ATA/ATAPI-4 or higher standard. Change of its value from 1 to 254 allows to regulate the performance of the hard disk drive and, thereby, to save energy of power supplies. Value less than 128 enables the hard disk drive to stop the spindle motor without any commands during certain period time, which allows saving as much energy of the power supply as possible, but leads to the increased deterioration of kinematics and the delay at the waking caused by waiting of magnetic disks spinning up to the necessary speed. The work of the advanced power management implemented in the hard disk drives does not depend on the "sleep" timer of the operating system.

Another EDIT: The cache on the 410 is enabled on all 4 drives. See here

[Metrik]

Disabling hibernation won't make the "Enable write cache" stick. I just tried it on my 212j with two WD20EARX. If that's any indication.

[jekyll]

Disabling hibernation won't make the "Enable write cache" stick. I just tried it on my 212j with two WD20EARX. If that's any indication.

I think you maybe misunderstood, some users have hibernation issues. I thought with the APM set@254, it may not let the drives hibernate.

[Metrik]

Ah, I understand now.

[Larry]

Another EDIT: The cache on the 410 is enabled on all 4 drives. See here

FWIW no problems here enabling the cache with dsm4.0 on my ds410 either. It's running four seagate 2tb ST2000DL003 drives. Hibernation is working ok too.

[synGuy]

Odd.
I'm running 2198 and all my write cache's seem to be ok:
sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA

I'm running 1x WD10EADS, 1x WD15EADS and 3x WD20EARS.

[tjkaz]

After reading this thread, I checked my settings after installing 2198.
I still have check marks for cache writing for both of my drives; wd20ears and wd30ezrs.

[joshuah]

Can you paste the disk section from /usr/syno/etc.defaults/scemd.xml. It appears that the 4.0 firmware has different content for this file for the different models of DS...which if true will be very strange indeed.

[sjeph8je]

Have been running with the write cache enabled and hibernation enabled with my WD20ears under DSM 3.2.
Now the write cache is disabled under DSM 4.0

[Metrik]

For the sake of proper comparison:

Does Enable write cache stick: No.
DS model: DS212j
Disk(s): 2 x WD20EARX in RAID-1
OS: DSM_DS212j_2198.pat

/usr/syno/etc.defaults/scemd.xml

Code: Select all

<disk_control>
        <disk model="ST9120821A">APM_255</disk>
        <disk model="HTS722020K9SA00">APM_255</disk>
        <disk model="ST980811AS">APM_255</disk>
        <disk model="MHV2060BH">APM_255</disk>
        <disk model="MK6034GSX">APM_254</disk>
        <disk model="ST9100824AS">APM_255</disk>
        <disk model="HM250JI">APM_255</disk>
        <disk model="MK1637GSX">APM_254</disk>
        <disk model="ST9100824AS">APM_255</disk>
        <disk model="ST9120822AS">APM_254</disk>
        <disk model="ST9160821AS">APM_254</disk>
        <disk model="WD2500BEVS-75UST0">APM_254</disk>
        <disk model="HM250JI">APM_254</disk>
        <disk model="WD2500BEVS">APM_254</disk>
        <disk model="WD1600BEVT">APM_255</disk>
        <disk model="HTS543232L9A300">APM_255</disk>
        <disk model="WD1600BEVE">APM_255</disk>
        <disk model="MK2546GSX">APM_254</disk>
        <disk model="MHV2080BHPL">APM_255</disk>
        <disk model="WD1200BEVE">APM_255</disk>
        <disk model="HTS543225L9A300">APM_255</disk>
        <disk model="WD3200BEVT">APM_254</disk>
        <disk model="MK8025GAS">APM_254</disk>
        <disk model="ST9200420AS">APM_254</disk>
        <disk model="WD3200BEVT">APM_254</disk>
        <disk model="HTS543216L9SA00">APM_254</disk>
        <disk model="MK4058GSX">APM_254</disk>
        <disk model="WD6400BEVT">APM_254</disk>
        <disk model="ST32000542AS">APM_255</disk>
        <disk model="ST95005620AS">APM_255</disk>
        <disk model="WD7500BPVT">APM_254</disk>
        <disk model="WD30EZRX">WCACHE_OFF</disk>
        <disk model="WD25EZRX">WCACHE_OFF</disk>
        <disk model="WD20EARX">WCACHE_OFF</disk>
        <disk model="WD15EARX">WCACHE_OFF</disk>
        <disk model="WD10EADX">WCACHE_OFF</disk>
        <disk model="WD7500AARX">WCACHE_OFF</disk>
        <disk model="WD30EZRSDTL">WCACHE_OFF</disk>
        <disk model="WD25EZRSDTL">WCACHE_OFF</disk>
        <disk model="WD20EARS">WCACHE_OFF</disk>
        <disk model="WD15EARS">WCACHE_OFF</disk>
        <disk model="WD10EARS">WCACHE_OFF</disk>
        <disk model="WD8000AARS">WCACHE_OFF</disk>
        <disk model="WD7500AARS">WCACHE_OFF</disk>
        <disk model="WD6400AARS">WCACHE_OFF</disk>
        <disk model="WD20EADS">WCACHE_OFF</disk>
        <disk model="WD15EADS">WCACHE_OFF</disk>
        <disk model="WD10EADS">WCACHE_OFF</disk>
        <disk model="WD8088AADS">WCACHE_OFF</disk>
        <disk model="WD7500AADS">WCACHE_OFF</disk>
        <disk model="WD6400AADS">WCACHE_OFF</disk>
        <disk model="WD5000AADS">WCACHE_OFF</disk>
        <disk model="WD3200AACS">WCACHE_OFF</disk>
        <disk model="ST32000542AS">WCACHE_OFF</disk>
        <disk model="ST31500541AS">WCACHE_OFF</disk>
        <disk model="ST31000520AS">WCACHE_OFF</disk>
        <disk model="ST3500412AS">WCACHE_OFF</disk>
</disk_control>