SAS or SATA disks

[Alessandro 123]

No, is not comparing a SAS 15k vs a SATA 7.2k disks.
Most vendor, particularry HGST has both interface for the same mechanical disk. In example, 7K600 series comes with SAS or SATA interfce.

It's the same disks, the only difference is the communication protocol.

What do you suggest? SAS seems to be more reliable (it should have T10 Protective Information for bit-rot protection, background media scan with error recovery and so on) but SMART support seems to be weak than SATA (much less info are reported)

Currently, I've always used SAS, even for 7.2k RPM disks, but these are much more difficult to order (in example, my current seller, has about 300 SATA 7K6000 and 0 SAS. The SAS ones must be ordered in 15-20 days)

Any suggestions ? I'm really thinking to move from SAS to SATA, for 7.2 high-capacity disks or, even better, move from HGST 7K6000 to WD Gold (both are enterprises disks, same failure rate, same capacity, same MTBF, same URE and so on). WD Gold are cheaper and our seller has 2000+ in stock currently (2 thousand) vs 300 (3 hundred)

 

[Klaus Steinberger]

if speed is not the problem, but capacity, you can use S-ATA Enterprise Disks also, we use many in 2 TByte + sizes.

SAS is a must on HA Filer configuration, where you want to failover disk pools between two heads.

SAS is faster for high speed SSD's as there is 12 GBit/s (and 24 Gbit/s coming soon).

 

[Alessandro 123]

I'm talking about spinning disks, as wrote, 7.2RPM.

If you read specs about HGST 7k6000 you'll see that both SAS and SATA are identical. The only difference is the communication protocol but it's the same mechanical disk.

I don't think that all SAS are dual-headed because the SAS disks i'm currenly using (the one defined as "near-line") is not seen as dual port by our SAS controller. Probably, only Enterprise SAS (not near-line) are dual headed but this is not my case.

ie: https://www.hgst.com/sites/default/files/resources/Ultrastar-7K6000-DS.pdf

 

[Klaus Steinberger]

SAS is always Dual Head, you will not see that with just one controller.

 

[udo]

Hi,
AFAIK the NCQ-Handling is better with an SAS-Disks (name TCQ by SAS) compared to the SATA version.
And the SAS connection is full duplex (but I think if you need the full bandwith read an write simultanous you have not really fast disk access with spindle disks).


Udo

 

[Rhinox]

SAS has definitely some advantages over SATA, i.e. better error recovery/reporting, full-duplex/half-duplex, higher signaling voltage (longer cables), etc...

 

[Alessandro 123]

SAS has definitely some advantages over SATA, i.e. better error recovery/reporting, full-duplex/half-duplex, higher signaling voltage (longer cables), etc...

Exactly what I've always thought, but this isn't true for error reporting.
SATA S.M.A.R.T. is much more details compared to the SAS one, with SAS disks you don't have any attribute to look for but only a generic "Elements in grown defect list"

You won't be able to know if disks is starting to trigger some seek errors, spin retry and so on. You don't have anything of this:

SMART Attributes Data Structure revision number: 16
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  1 Raw_Read_Error_Rate     0x002f   200   200   051    Pre-fail  Always       -       0
  3 Spin_Up_Time            0x0027   100   253   021    Pre-fail  Always       -       0
  4 Start_Stop_Count        0x0032   100   100   000    Old_age   Always       -       3
  5 Reallocated_Sector_Ct   0x0033   200   200   140    Pre-fail  Always       -       0
  7 Seek_Error_Rate         0x002e   200   200   000    Old_age   Always       -       0
  9 Power_On_Hours          0x0032   080   080   000    Old_age   Always       -       15322
 10 Spin_Retry_Count        0x0032   100   253   000    Old_age   Always       -       0
 11 Calibration_Retry_Count 0x0032   100   253   000    Old_age   Always       -       0
 12 Power_Cycle_Count       0x0032   100   100   000    Old_age   Always       -       3
192 Power-Off_Retract_Count 0x0032   200   200   000    Old_age   Always       -       1
193 Load_Cycle_Count        0x0032   200   200   000    Old_age   Always       -       43
194 Temperature_Celsius     0x0022   116   108   000    Old_age   Always       -       27
196 Reallocated_Event_Count 0x0032   200   200   000    Old_age   Always       -       0
197 Current_Pending_Sector  0x0032   200   200   000    Old_age   Always       -       0
198 Offline_Uncorrectable   0x0030   200   200   000    Old_age   Offline      -       0
199 UDMA_CRC_Error_Count    0x0032   200   200   000    Old_age   Always       -       0
200 Multi_Zone_Error_Rate   0x0008   200   200   000    Old_age   Offline      -       0

 

[Rhinox]

By "error reporting and recovery" I mean errors concerning data stored on disk. Not everything in SMART is error reporting (i.e. load-cycles, writes, temperature, etc). Moreover, SAS is using SCSI-commands for error reporting and recovery, which is by far superior over SMART used in SATA-drives.

I'm not going deep into details (you can find many "sas vs sata" articles on internet if you want). Simply put, if slightly higher price is not problem, go for SAS.

 

[Alessandro 123]

Price is not a problem. SAS or SATA are priced about the same for this kind of disk (maybe a couple of euros more)

Availability is the real issue. Out sellers doesn't have SAS model in stock and next batch is expected for end of May while SATA are immediatly availability in thousands pieces

 

[Alessandro 123]

Anyway what really i don't understand is how to read smartctl output on SAS disks. Official smartctl docs doesn't say much about SCSI devices