Q & A on raid and bbu

In the past few days, the write policy of the RAID card is switched back to WT from WB. If "Learn cycle" occurs during business peaks, it will seriously affect the performance of the database. After the problem is solved, sort out your understanding of these problems. I will not describe the megacli command set I have used. There are a lot of information about it on the Internet. We recommend related articles by Tan and ye from Chinese documents.

I will explain the problems related to the RAID card bbu through Q &:

Q1: How many methods can the RAID card (megaraid SAS 8708elp) of the faulty server be managed?
1. You can manage raid arrays in the following three ways:
A) megaraid Storage Manager (method: press Ctrl + R to enter the array card BIOS settings when the system boot screen is displayed)
B) webbios (method: press Ctrl + H to enter the management interface when the system boot screen is displayed)
C) megacli (method: Based on nearline)

Q2: Why does the effective write policy take effect on the first day of each newly installed server write through instead of setting the (default) write back?
1. The existence of bbu is a necessary condition for using writeback;
2. Write-back is the default write policy;
3. After the raid array and ibbu are deployed, ibbu completes learn cycle at least six hours during its first use.
4. One learn cycle includes two parts:
A) Learn cycle discharge cycle: approximately three hours
B) Learn cycle charge cycle: approximately four hours

Q3: after the power is fully charged, write back is also in normal use. But after a while, why is the write policy automatically switched back to write through?
1. Write Through policy will be used in three cases. First, write through policy is set. (haha, This is not nonsense !) 2. No battery or battery is faulty; 3. Battery is in the "low-charge state" phase. What is "low-charge state "? Simply put, when the battery power is insufficient to maintain 24 hours of data, it will switch the previously set write back to write through, this behavior occurs in the "discharge cycle" step of "Learn cycle" because battery's power meets "low-charge state" during the "discharge cycle" process ". Note: it does not mean that when battery's power is sufficient, it will automatically switch back to write back after 24 hours data requirements are ensured, switching from write through to write back occurs after battery is full (> = 85% ).

Q4: How long does battery of bbu retain data?
72 hours

Q5: How long does learn cycle take?
About three months, that is, about 90 days.

Q6: What is the normal temperature of battery?
Operating temperature maximum ambient: 50 degrees Celsius (40 degrees Celsius w/ibbu), it should be noted that during charging, the battery temperature will be 10 ~ higher than usual ~ About 15 degrees.

Q7: How can I deal with such incidents?
There are two solutions:
A) obtain the next charge and discharge time based on the log information (figure 1). charge and discharge are performed in advance when the traffic volume is low to avoid the write policy change during the service peak period.

T4: *** battery feature properties ***
T4 :_________________________________________________

T4: auto learn period: 30 days
T4: next learn time: 322829199
T4: Battery ID: 38d707d5
T4: delayed learn interval: 0 hours from scheduled time
T4: autolearnmode: 0
T4: next learn cheduled on: 03 25 2010
T4 :_________________________________________________

Figure 1

B) use forced write-back, that is, the so-called force WB with no battery. Of course, if you want to set it to it, the server should have backup power such as UPS.