令和6年度 ITパスポート試験問38

This question's explanation and your answers so far.

問38

頻出度★★★

あるシステムの運用において, 利用者との間で SLA を交わし, 利用可能日を月曜日から金曜日, 1日の利用可能時間を7時から22時まで, 稼働率を98%以上で合意した。 1週間の運用において, 障害などでシステムの停止を許容できる時間は最大何時間か。

出典　令和6年度 ITパスポート試験問38

解説

問 38

Incorrectア
0.3 hours is the value calculated using only one day of operating time, 15 hours (15×0.02=0.3). The question asks for the allowable downtime over “one week of operation”, so the basis must be 5 days = 75 hours; thus this is incorrect.
イ
正解 The available hours per day are from 7:00 to 22:00, which is 22−7=15 hours, and the available days are the 5 days from Monday to Friday, so the total operating time over one week is 15 hours × 5 days = 75 hours. To meet an availability rate of 98% or higher, the downtime must be kept within 2% (=100%−98%) of the total. Therefore the maximum allowable downtime is 75 hours × (1−0.98) = 75 × 0.02 = 1.5 hours, so “イ” is correct.
Incorrectウ
1.8 hours is the value calculated by treating the operating days as 6 days (15×6=90 hours) (90×0.02=1.8). The available days agreed in the SLA are the 5 days from Monday to Friday, so taking it as 6 days misreads the condition and is incorrect.
Incorrectエ
2.1 hours is the value calculated by treating one week as 7 days (15×7=105 hours) (105×0.02=2.1). Saturday and Sunday are not included in the available days and the operating days are 5, so calculating with 7 days is incorrect.

ここがポイント

Availability = uptime ÷ total operating time. The allowable downtime is found by “total operating time × (1 − availability)”.
The total operating time is calculated from the available number of days and the available hours per day agreed in the SLA (in this question, 15 hours × 5 days = 75 hours, excluding weekends and nighttime).

用語

解答問38イ