[mythtv-users] best use of limited RAM

Wed Nov 22 18:57:45 UTC 2017

On Wednesday, November 22, 2017 19:01 CET, Keith Pyle <kpyle at austin.rr.com> wrote:
 On 11/22/17 08:17, Marius Schrecker wrote:
> ? I am repurposing an old, box that was previously used as a combined mythtv backend/frontend, Logitech Media Server and nfs fileserver as a mythtv backend only.
>
> The system has a maximum of 8GB RAM, a quite well used 120GB SSD (no signs of failure yet) and I just replaced the 3TB media storage spindle drive with a new 4TB unit.
>
> My main concern is offloading the SSD as much as possible to prolong its life.

Marius,

Mike's comments are quite correct. Look in your smartctl output for a
line similar to this:

ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE
UPDATED WHEN_FAILED RAW_VALUE

233 Media_Wearout_Indicator 0x0032 098 098 000 Old_age
Always - 0

Many SSD's include this metric as an indicator of how much wear leveling
has been done (strictly speaking, it's a NAND erase cycle metric).
Intel defined this metric for their SSD's, but I've seen it on non-Intel
drives too. A new drive should show a value of 100. A value of 1
means the drive has reached its designed write cycle limit, but it may
well continue working past that point. The value is a linear function
of the write/erase cycle count.

The line above is for an 80 GB Intel MLC SSD that has 72000 hours of use
(8 years) in my Myth backend as the OS and DB drive. It shows total
writes of just under 7 TB. It was at ~62000 hours of use that it
dropped from 99 to 98. So, for a pure backend, a decent SSD will work
fine for a very long time. It may well die due to other failures long
before reaching a write limit. For my backend workload, this drive's
flash should have another 300+ years. :-)

With regard to memory, Linux will happily use whatever you provide for
caching. The right amount of caching is highly dependent on what you
run. If your workload involves frequently reading the same data many
times, you'll benefit from having enough memory to keep that frequently
accessed data in cache. For a Myth backend that runs commflag jobs, it
can help to have the video data still in memory rather than re-reading
it from disk.

My backend runs Myth, mysql, and apache. It has 4 GB and typically has
1.0-1.5 GB in the "used" category. That leaves 2.5-3.0 GB being used
for cache and I don't see any signs of the system being resource stressed.

Keith
 Thanks Keith,

  My drive doesn't seem to display that metric, but one or two others seem to suggest that there'e plenty of life left. Here's the table again:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  1 Raw_Read_Error_Rate     0x0033   120   120   050    Pre-fail  Always       -       0/0
  5 Retired_Block_Count     0x0033   100   100   003    Pre-fail  Always       -       0
  9 Power_On_Hours_and_Msec 0x0032   084   084   000    Old_age   Always       -       14095h+59m+25.710s
 12 Power_Cycle_Count       0x0032   100   100   000    Old_age   Always       -       103
171 Program_Fail_Count      0x000a   000   000   000    Old_age   Always       -       0
172 Erase_Fail_Count        0x0032   000   000   000    Old_age   Always       -       0
174 Unexpect_Power_Loss_Ct  0x0030   000   000   000    Old_age   Offline      -       37
177 Wear_Range_Delta        0x0000   000   000   000    Old_age   Offline      -       1
181 Program_Fail_Count      0x000a   000   000   000    Old_age   Always       -       0
182 Erase_Fail_Count        0x0032   000   000   000    Old_age   Always       -       0
187 Reported_Uncorrect      0x0012   100   100   000    Old_age   Always       -       0
189 Airflow_Temperature_Cel 0x0000   017   043   000    Old_age   Offline      -       17 (Min/Max 8/43)
194 Temperature_Celsius     0x0022   017   043   000    Old_age   Always       -       17 (Min/Max 8/43)
195 ECC_Uncorr_Error_Count  0x001c   120   120   000    Old_age   Offline      -       0/0
196 Reallocated_Event_Count 0x0033   100   100   003    Pre-fail  Always       -       0
201 Unc_Soft_Read_Err_Rate  0x001c   120   120   000    Old_age   Offline      -       0/0
204 Soft_ECC_Correct_Rate   0x001c   120   120   000    Old_age   Offline      -       0/0
230 Life_Curve_Status       0x0013   100   100   000    Pre-fail  Always       -       100
231 SSD_Life_Left           0x0013   100   100   010    Pre-fail  Always       -       0
233 SandForce_Internal      0x0032   000   000   000    Old_age   Always       -       1445
234 SandForce_Internal      0x0032   000   000   000    Old_age   Always       -       729
241 Lifetime_Writes_GiB     0x0032   000   000   000    Old_age   Always       -       729
242 Lifetime_Reads_GiB      0x0032   000   000   000    Old_age   Always       -       189

BR.

-Marius--

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