Cache Policy's are how the raid card uses on board RAM to collect data before writing out to disk or to read data before the system asks for it.
Write cache is used when we have a lot of data to write and it is faster to write data sequentially to disk instead of writing small chunks.
Read cache is used when the system has asked for some data and the raid card keeps the data in cache in case the system asks for the same data again.
It is always faster to read and write to cache then to access spinning disks. Understand that you should only use caching if you have good UPS power to the system.
If the system looses power and does not flush the cache it is possible to loose data. No one wants that. Lets look at each cache policy LSI raid card use.
WriteBack uses the card's cache to collect enough data to make a series of long sequential writes out to disk. This is the fastest write method. WriteThrough tells the card to write all data directly to disk without cache. This method is quite slow by about 1/10 the speed of WriteBack, but is safer as no data can be lost that was in cache when the machine's power fails. ReadAdaptive uses an algorithm to see if when the OS asks for a bunch of data blocks sequentially, if we should read a few more sequential blocks because the OS _might_ ask for those too. This method can lead to good speed increases. ReadAheadNone tells the raid card to only read the data off the raid disk if it was actually asked for. No more, no less. Cached allows the general use of the cards cache for any data which is read or written. Very efficient if the same data is accessed over and over again. Direct is straight access to the disk without ever storing data in the cache. This can be slow as any I/O has to touch the disk platters. Write Cache OK if Bad BBU tells the card to use write caching even if the Battery Backup Unit (BBU) is bad, disabled or missing. This is a good setting if your raid card's BBU charger is bad, if you do not want or can't to replace the BBU or if you do not want WriteThrough enabled during a BBU relearn test.
No Write Cache if Bad BBU if the BBU is not available for any reason then disable WriteBack and turn on WriteThrough. This option is safer for your data, but the raid card will switch to WriteThrough during a battery relearn cycle. Disk Cache Policy: Enabled Use the hard drive's own cache. For example if data is written out the drives this option lets the drives themselves cache data internally before writing data to its platters. Disk Cache Policy: Disabled does not allow the drive to use any of its own internal cache.
============================================================================== Versions ================ Product Name : SAS3108 Serial No : FW Package Build: 24.1.1-0035
Mfg. Data ================ Mfg. Date : 00/00/00 Rework Date : 00/00/00 Revision No : Battery FRU : N/A
Image Versions in Flash: ================ BIOS Version : 6.13.00.2_4.14.05.00_0x06010602 FW Version : 4.210.90-3396 NVDATA Version : 3.1310.00-0067 Ctrl-R Version : 5.01-0008 Boot Block Version : 3.00.00.00-0009
Pending Images in Flash ================ None
PCI Info ================ Controller Id : 0000 Vendor Id : 1000 Device Id : 005d SubVendorId : 19e5 SubDeviceId : d207
Host Interface : PCIE
ChipRevision : C0
Link Speed : 0 Number of Frontend Port: 0 Device Interface : PCIE
Number of Backend Port: 8 Port : Address 0 500e004aaaaaaa1f 1 0000000000000000 2 0000000000000000 3 0000000000000000 4 0000000000000000 5 0000000000000000 6 0000000000000000 7 0000000000000000
HW Configuration ================ SAS Address : 5101b5442bcc7000 BBU : Absent Alarm : Present NVRAM : Present Serial Debugger : Present Memory : Present Flash : Present Memory Size : 1024MB TPM : Absent On board Expander: Absent Upgrade Key : Absent Temperature sensor for ROC : Present Temperature sensor for controller : Absent
ROC temperature : 66 degree Celsius
Settings ================ Current Time : 20:29:55 9/12, 2019 Predictive Fail Poll Interval : 300sec Interrupt Throttle Active Count : 16 Interrupt Throttle Completion : 50us Rebuild Rate : 30% PR Rate : 30% BGI Rate : 30% Check Consistency Rate : 30% Reconstruction Rate : 30% Cache Flush Interval : 4s Max Drives to Spinup at One Time : 4 Delay Among Spinup Groups : 2s Physical Drive Coercion Mode : 1GB Cluster Mode : Disabled Alarm : Enabled Auto Rebuild : Enabled Battery Warning : Enabled Ecc Bucket Size : 15 Ecc Bucket Leak Rate : 1440 Minutes Restore HotSpare on Insertion : Enabled Expose Enclosure Devices : Enabled Maintain PD Fail History : Enabled Host Request Reordering : Enabled Auto Detect BackPlane Enabled : SGPIO/i2c SEP Load Balance Mode : Auto Use FDE Only : No Security Key Assigned : No Security Key Failed : No Security Key Not Backedup : No Default LD PowerSave Policy : Controller Defined Maximum number of direct attached drives to spin up in 1 min : 120 Auto Enhanced Import : No Any Offline VD Cache Preserved : No Allow Boot with Preserved Cache : No Disable Online Controller Reset : No PFK in NVRAM : No Use disk activity for locate : No POST delay : 90 seconds BIOS Error Handling : Stop On Errors Current Boot Mode :Normal Capabilities ================ RAID Level Supported : RAID0, RAID1, RAID5, RAID6, RAID00, RAID10, RAID50, RAID60, PRL 11, PRL 11 with spanning, SRL 3 supported, PRL11-RLQ0 DDF layout with no span, PRL11-RLQ0 DDF layout with span Supported Drives : SAS, SATA
Allowed Mixing:
Mix in Enclosure Allowed Mix of SAS/SATA of HDD type in VD Allowed
Status ================ ECC Bucket Count : 0
Limitations ================ Max Arms Per VD : 32 Max Spans Per VD : 8 Max Arrays : 128 Max Number of VDs : 64 Max Parallel Commands : 928 Max SGE Count : 60 Max Data Transfer Size : 8192 sectors Max Strips PerIO : 42 Max LD per array : 16 Min Strip Size : 64 KB Max Strip Size : 1.0 MB Max Configurable CacheCade Size: 0 GB Current Size of CacheCade : 0 GB Current Size of FW Cache : 837 MB
Supported Adapter Operations ================ Rebuild Rate : Yes CC Rate : Yes BGI Rate : Yes Reconstruct Rate : Yes Patrol Read Rate : Yes Alarm Control : Yes Cluster Support : No BBU : Yes Spanning : Yes Dedicated Hot Spare : Yes Revertible Hot Spares : Yes Foreign Config Import : Yes Self Diagnostic : Yes Allow Mixed Redundancy on Array : No Global Hot Spares : Yes Deny SCSI Passthrough : No Deny SMP Passthrough : No Deny STP Passthrough : No Support Security : No Snapshot Enabled : No Support the OCE without adding drives : Yes Support PFK : Yes Support PI : Yes Support Boot Time PFK Change : No Disable Online PFK Change : No Support LDPI Type1 : No Support LDPI Type2 : No Support LDPI Type3 : No PFK TrailTime Remaining : 0 days 0 hours Support Shield State : Yes Block SSD Write Disk Cache Change: No Support Online FW Update : Yes
Supported VD Operations ================ Read Policy : Yes Write Policy : Yes IO Policy : Yes Access Policy : Yes Disk Cache Policy : Yes Reconstruction : Yes Deny Locate : No Deny CC : No Allow Ctrl Encryption: No Enable LDBBM : No Support Breakmirror : No Power Savings : No
Supported PD Operations ================ Force Online : Yes Force Offline : Yes Force Rebuild : Yes Deny Force Failed : No Deny Force Good/Bad : No Deny Missing Replace : No Deny Clear : No Deny Locate : No Support Temperature : Yes Disable Copyback : No Enable JBOD : No Enable Copyback on SMART : Yes Enable Copyback to SSD on SMART Error : Yes Enable SSD Patrol Read : No PR Correct Unconfigured Areas : Yes Enable Spin Down of UnConfigured Drives : Yes Disable Spin Down of hot spares : No Spin Down time : 30 T10 Power State : No Error Counters ================ Memory Correctable Errors : 0 Memory Uncorrectable Errors : 0
Cluster Information ================ Cluster Permitted : No Cluster Active : No
Default Settings ================ Phy Polarity : 0 Phy PolaritySplit : 0 Background Rate : 30 Strip Size : 256kB Flush Time : 4 seconds Write Policy : WB Read Policy : Adaptive Cache When BBU Bad : Disabled Cached IO : No SMART Mode : Mode 6 Alarm Disable : Yes Coercion Mode : 1GB ZCR Config : Unknown Dirty LED Shows Drive Activity : No BIOS Continue on Error : 0 Spin Down Mode : None Allowed Device Type : SAS/SATA Mix Allow Mix in Enclosure : Yes Allow HDD SAS/SATA Mix in VD : Yes Allow SSD SAS/SATA Mix in VD : No Allow HDD/SSD Mix in VD : No Allow SATA in Cluster : No Max Chained Enclosures : 16 Disable Ctrl-R : No Enable Web BIOS : No Direct PD Mapping : No BIOS Enumerate VDs : Yes Restore Hot Spare on Insertion : Yes Expose Enclosure Devices : Yes Maintain PD Fail History : Yes Disable Puncturing : No Zero Based Enclosure Enumeration : No PreBoot CLI Enabled : No LED Show Drive Activity : No Cluster Disable : Yes SAS Disable : No Auto Detect BackPlane Enable : SGPIO/i2c SEP Use FDE Only : No Enable Led Header : Yes Delay during POST : 0 EnableCrashDump : No Disable Online Controller Reset : No EnableLDBBM : No Un-Certified Hard Disk Drives : Allow Treat Single span R1E as R10 : No Max LD per array : 16 Power Saving option : Don't Auto spin down Configured Drives Max power savings option is not allowed for LDs. Only T10 power conditions are to be used. Default spin down time in minutes: 30 Enable JBOD : No TTY Log In Flash : No Auto Enhanced Import : No BreakMirror RAID Support : No Disable Join Mirror : Yes Enable Shield State : Yes Time taken to detect CME : 60s
Exit Code: 0x00
这里信息很多，目前关注到：
Product Name是 SAS3108，如前所述，从官网查得它是一个RoC型号；
Number of Frontend Port是0；Number of Backend Port是8；（这是什么意思？前端通过PCIe连server，后端可以连至多8个Disk Enclosure？）
Enclosure 0: Device ID : 14 Number of Slots : 16 Number of Power Supplies : 2 Number of Fans : 4 Number of Temperature Sensors : 4 Number of Alarms : 1 Number of SIM Modules : 1 Number of Physical Drives : 14 Status : Normal Position : 1 Connector Name : Port A Enclosure type : SES FRU Part Number : N/A Enclosure Serial Number : N/A ESM Serial Number : N/A Enclosure Zoning Mode : N/A Partner Device Id : 65535
Inquiry data : Vendor Identification : 12G SAS Product Identification : Expander Product Revision Level : RevB Vendor Specific :
Number of Voltage Sensors :0
Number of Power Supplies : 2
Power Supply : 0 Power Supply Status : Unsupported
Power Supply : 1 Power Supply Status : Unsupported
Number of Fans : 4
Fan : 0 Fan Status : Unsupported
Fan : 1 Fan Status : Unsupported
Fan : 2 Fan Status : Unsupported
Fan : 3 Fan Status : Unsupported
Number of Temperature Sensors : 4
Temp Sensor : 0 Temperature : 236 Temperature Sensor Status : Unsupported
Temp Sensor : 1 Temperature : 236 Temperature Sensor Status : Unsupported
Temp Sensor : 2 Temperature : 236 Temperature Sensor Status : Unsupported
Temp Sensor : 3 Temperature : 236 Temperature Sensor Status : Unsupported
Number of Chassis : 1
Chassis : 0 Chassis Status : OK
Enclosure 1: Device ID : 252 Number of Slots : 8 Number of Power Supplies : 0 Number of Fans : 0 Number of Temperature Sensors : 0 Number of Alarms : 0 Number of SIM Modules : 1 Number of Physical Drives : 0 Status : Normal Position : 1 Connector Name : Unavailable Enclosure type : SGPIO FRU Part Number : N/A Enclosure Serial Number : N/A ESM Serial Number : N/A Enclosure Zoning Mode : N/A Partner Device Id : Unavailable
Inquiry data : Vendor Identification : LSI Product Identification : SGPIO Product Revision Level : N/A Vendor Specific :
Raw Size: 3.638 TB [0x1d1c0beb0 Sectors] Non Coerced Size: 3.637 TB [0x1d1b0beb0 Sectors] Coerced Size: 3.637 TB [0x1d1a94800 Sectors] Sector Size: 512 Logical Sector Size: 512 Physical Sector Size: 512 Firmware state: Online, Spun Up Commissioned Spare : No Emergency Spare : No Device Firmware Level: A8B0 Shield Counter: 0 Successful diagnostics completion on : N/A SAS Address(0): 0x500e004aaaaaaa00 Connected Port Number: 0(path0) Inquiry Data: PN1334PEG8KTEXHGST HUS724040ALA640 MFAOA8B0 FDE Capable: Not Capable FDE Enable: Disable Secured: Unsecured Locked: Unlocked Needs EKM Attention: No Foreign State: None Device Speed: 6.0Gb/s Link Speed: 6.0Gb/s Media Type: Hard Disk Device Drive: Not Certified Drive Temperature :30C (86.00 F) PI Eligibility: No Drive is formatted for PI information: No PI: No PI Port-0 : Port status: Active Port's Linkspeed: 6.0Gb/s Drive has flagged a S.M.A.R.T alert : No
Raw Size: 279.396 GB [0x22ecb25c Sectors] Non Coerced Size: 278.896 GB [0x22dcb25c Sectors] Coerced Size: 278.464 GB [0x22cee000 Sectors] Sector Size: 512 Logical Sector Size: 512 Physical Sector Size: 512 Firmware state: Online, Spun Up Commissioned Spare : No Emergency Spare : No Device Firmware Level: A440 Shield Counter: 0 Successful diagnostics completion on : N/A SAS Address(0): 0x5000cca06e20bddd SAS Address(1): 0x0 Connected Port Number: 0(path0) Inquiry Data: HITACHI HUC109030CSS600 A440W5GL06HB FDE Capable: Not Capable FDE Enable: Disable Secured: Unsecured Locked: Unlocked Needs EKM Attention: No Foreign State: None Device Speed: 6.0Gb/s Link Speed: 6.0Gb/s Media Type: Hard Disk Device Drive: Not Certified Drive Temperature :40C (104.00 F) PI Eligibility: No Drive is formatted for PI information: No PI: No PI Port-0 : Port status: Active Port's Linkspeed: 6.0Gb/s Port-1 : Port status: Active Port's Linkspeed: 6.0Gb/s Drive has flagged a S.M.A.R.T alert : No
Virtual Drive: 0 (Target Id: 0) Name : RAID Level : Primary-1, Secondary-0, RAID Level Qualifier-0 Size : 278.464 GB Sector Size : 512 Is VD emulated : No Mirror Data : 278.464 GB State : Optimal Strip Size : 256 KB Number Of Drives : 2 Span Depth : 1 Default Cache Policy: WriteBack, ReadAhead, Direct, No Write Cache if Bad BBU Current Cache Policy: WriteThrough, ReadAhead, Direct, No Write Cache if Bad BBU Default Access Policy: Read/Write Current Access Policy: Read/Write Disk Cache Policy : Disk's Default Encryption Type : None PI type: No PI
Is VD Cached: No
Virtual Drive: 1 (Target Id: 1) Name : RAID Level : Primary-0, Secondary-0, RAID Level Qualifier-0 Size : 3.637 TB Sector Size : 512 Is VD emulated : No Parity Size : 0 State : Optimal Strip Size : 256 KB Number Of Drives : 1 Span Depth : 1 Default Cache Policy: WriteBack, ReadAdaptive, Direct, Write Cache OK if Bad BBU Current Cache Policy: WriteBack, ReadAdaptive, Direct, Write Cache OK if Bad BBU Default Access Policy: Read/Write Current Access Policy: Read/Write Disk Cache Policy : Disk's Default Encryption Type : None PI type: No PI
Is VD Cached: No
Virtual Drive: 2 (Target Id: 2) ......
Virtual Drive: 3 (Target Id: 3) ......
Virtual Drive: 4 (Target Id: 4) ......
Virtual Drive: 5 (Target Id: 5) ......
Virtual Drive: 6 (Target Id: 6) ......
Virtual Drive: 7 (Target Id: 7) ......
Virtual Drive: 8 (Target Id: 8) ......
Virtual Drive: 9 (Target Id: 9) ......
Virtual Drive: 10 (Target Id: 10) ......
Virtual Drive: 11 (Target Id: 11) ......
Virtual Drive: 12 (Target Id: 12) ......
Exit Code: 0x00
如第2.4.3节所述，此MegaRAID卡上有13个Virtual Drives。
第1个是Virtual Drive: 0 (Target Id: 0)：RAID Level是Primary-1, Secondary-0（即RAID-10）；使用2个Physical Drive（Number Of Drives为2）。Cache Policy是WriteThrough, ReadAhead, Direct, No Write Cache if Bad BBU；Disk Cache Policy是Disk's Default；
其他和Virtual Drive: 1 (Target Id: 1)一样：RAID Level是Primary-0, Secondary-0（即RAID-0）；使用1个Physical Drive（Number Of Drives为1）。Cache Policy是WriteBack, ReadAdaptive, Direct, Write Cache OK if Bad BBU；
注意Virtual Drive: 0 (Target Id: 0)是系统盘，Level是RAID-10，并且Cache Policy更安全（包括WriteThrough, No Write Cache if Bad BBU）；其他Virtual Drive是数据盘，Level是RAID-0，Cache Policy也不如系统盘安全（包括WriteBack, Write Cache OK if Bad BBU）；
Virtual Drive: 0 (Target Id: 0) Name : RAID Level : Primary-1, Secondary-0, RAID Level Qualifier-0 Size : 278.464 GB Sector Size : 512 Is VD emulated : No Mirror Data : 278.464 GB State : Optimal Strip Size : 256 KB Number Of Drives : 2 Span Depth : 1 Default Cache Policy: WriteBack, ReadAhead, Direct, No Write Cache if Bad BBU Current Cache Policy: WriteThrough, ReadAhead, Direct, No Write Cache if Bad BBU Default Access Policy: Read/Write Current Access Policy: Read/Write Disk Cache Policy : Disk's Default Encryption Type : None PI type: No PI
Is VD Cached: No Number of Spans: 1 Span: 0 - Number of PDs: 2
Raw Size: 279.396 GB [0x22ecb25c Sectors] Non Coerced Size: 278.896 GB [0x22dcb25c Sectors] Coerced Size: 278.464 GB [0x22cee000 Sectors] Sector Size: 512 Logical Sector Size: 512 Physical Sector Size: 512 Firmware state: Online, Spun Up Commissioned Spare : No Emergency Spare : No Device Firmware Level: A440 Shield Counter: 0 Successful diagnostics completion on : N/A SAS Address(0): 0x5000cca06e20bddd SAS Address(1): 0x0 Connected Port Number: 0(path0) Inquiry Data: HITACHI HUC109030CSS600 A440W5GL06HB FDE Capable: Not Capable FDE Enable: Disable Secured: Unsecured Locked: Unlocked Needs EKM Attention: No Foreign State: None Device Speed: 6.0Gb/s Link Speed: 6.0Gb/s Media Type: Hard Disk Device Drive: Not Certified Drive Temperature :40C (104.00 F) PI Eligibility: No Drive is formatted for PI information: No PI: No PI Port-0 : Port status: Active Port's Linkspeed: 6.0Gb/s Port-1 : Port status: Active Port's Linkspeed: 6.0Gb/s Drive has flagged a S.M.A.R.T alert : No
Raw Size: 279.396 GB [0x22ecb25c Sectors] Non Coerced Size: 278.896 GB [0x22dcb25c Sectors] Coerced Size: 278.464 GB [0x22cee000 Sectors] Sector Size: 512 Logical Sector Size: 512 Physical Sector Size: 512 Firmware state: Online, Spun Up Commissioned Spare : No Emergency Spare : No Device Firmware Level: A440 Shield Counter: 0 Successful diagnostics completion on : N/A SAS Address(0): 0x5000cca06e20c9b5 SAS Address(1): 0x0 Connected Port Number: 0(path0) Inquiry Data: HITACHI HUC109030CSS600 A440W5GL0ZYB FDE Capable: Not Capable FDE Enable: Disable Secured: Unsecured Locked: Unlocked Needs EKM Attention: No Foreign State: None Device Speed: 6.0Gb/s Link Speed: 6.0Gb/s Media Type: Hard Disk Device Drive: Not Certified Drive Temperature :40C (104.00 F) PI Eligibility: No Drive is formatted for PI information: No PI: No PI Port-0 : Port status: Active Port's Linkspeed: 6.0Gb/s Port-1 : Port status: Active Port's Linkspeed: 6.0Gb/s Drive has flagged a S.M.A.R.T alert : No
Virtual Drive: 1 (Target Id: 1) Name : RAID Level : Primary-0, Secondary-0, RAID Level Qualifier-0 Size : 3.637 TB Sector Size : 512 Is VD emulated : No Parity Size : 0 State : Optimal Strip Size : 256 KB Number Of Drives : 1 Span Depth : 1 Default Cache Policy: WriteBack, ReadAdaptive, Direct, Write Cache OK if Bad BBU Current Cache Policy: WriteBack, ReadAdaptive, Direct, Write Cache OK if Bad BBU Default Access Policy: Read/Write Current Access Policy: Read/Write Disk Cache Policy : Disk's Default Encryption Type : None PI type: No PI
Is VD Cached: No Number of Spans: 1 Span: 0 - Number of PDs: 1
Raw Size: 3.638 TB [0x1d1c0beb0 Sectors] Non Coerced Size: 3.637 TB [0x1d1b0beb0 Sectors] Coerced Size: 3.637 TB [0x1d1a94800 Sectors] Sector Size: 512 Logical Sector Size: 512 Physical Sector Size: 512 Firmware state: Online, Spun Up Commissioned Spare : No Emergency Spare : No Device Firmware Level: A8B0 Shield Counter: 0 Successful diagnostics completion on : N/A SAS Address(0): 0x500e004aaaaaaa00 Connected Port Number: 0(path0) Inquiry Data: PN1334PEG8KTEXHGST HUS724040ALA640 MFAOA8B0 FDE Capable: Not Capable FDE Enable: Disable Secured: Unsecured Locked: Unlocked Needs EKM Attention: No Foreign State: None Device Speed: 6.0Gb/s Link Speed: 6.0Gb/s Media Type: Hard Disk Device Drive: Not Certified Drive Temperature :30C (86.00 F) PI Eligibility: No Drive is formatted for PI information: No PI: No PI Port-0 : Port status: Active Port's Linkspeed: 6.0Gb/s Drive has flagged a S.M.A.R.T alert : No
