[mythtv-users] best use of limited RAM

Mike Hodson mystica at gmail.com
Wed Nov 22 21:18:41 UTC 2017


On Wed, Nov 22, 2017 at 4:13 PM, Mike Hodson <mystica at gmail.com> wrote:

> Hello again Marius,
>
> Looking at the SMART data, it is indeed a Sandforce drive;  these have the
> added benefit of lessened write-cycles due to onboard LZO(or similar; its
> proprietary but seems like LZO to me) compression internal to the chipset
> firmware.
>
> Thats where these 5 values come into play:
>
> 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
>
> 233 is "actual bytes over the SATA Bus written"; 234 is "bytes after
> compression" and it should almost always match 241 "Lifetime Writes" which
> is directly to the NAND. Reads is even lower.
>
> 231 is the Sandforce numbered metric similar to the aforementioned 233
> Media_Wearout_Indicator metric.  Different numbers, same basic principle.
> You're still at 100/100 which is still "pretty close to new" in the grand
> scheme of things.
>
> My own 60GB Sandforce drive has way more writes/reads than yours, nearly
> triple for 1/2 the amount of NAND Onboard.
>
> 195 ECC_Uncorr_Error_Count  0x001c   120   120   000    Old_age   Offline
>     -       0/0
> 196 Reallocated_Event_Count 0x0033   100   100   000    Pre-fail  Always
>      -       0
> 231 SSD_Life_Left           0x0013   100   100   010    Pre-fail  Always
>      -       0
> 233 SandForce_Internal      0x0000   000   000   000    Old_age   Offline
>     -       3520
> 234 SandForce_Internal      0x0032   000   000   000    Old_age   Always
>      -       3904
> 241 Lifetime_Writes_GiB     0x0032   000   000   000    Old_age   Always
>      -       3904
> 242 Lifetime_Reads_GiB      0x0032   000   000   000    Old_age   Always
>      -       10944
>
> As this shows, my write-load hasn't been so easily LZO compressed, and
> internal wear-leveling has made the 'write amplification' about 1.1 the
> input bytes.  3.9TiB written to the flash, over its lifecycle with only 3.5
> TiB of input data.   Yours shows the approximate 1/2 write reduction
> possible when the majority of files on the drive are textual or easily
> compressed.  I've written a lot of already-compressed data to the disk over
> its lifetime, doing many Gentoo package updates and compiles, which implies
> a ton of bz2/xz files written over the years.
>
> Both of our 'worst case scenario' disks should still last long into next
> decade as long as the electronics don't die first :)
>
> Mike
>
>
> I should also mention the 2 other metrics I posted:  195 ECC errors, and
196 reallocated sector count.  These are the 2 values that will start to
rise before 'actual' drive death due to NAND failure. Indeed the
SSD_Life_Left metric is specifically a linear 'how many is the drive rated
for / how many have occurred' erase-count equation.

The spontaneous ECC errors and reallocations are more indicative to the
NAND's actual health.  Having 0 of either, you're still doing fine.

Mike
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