EC2インスタンスに何個EBSがつけられるの？
Amazon Web Service (AWS) で 一つのEC2インスタンスに何個 EBS がくっつけられるのかマニュアルを探してみたけれど、以下の記載しかなくどうもはっきりしたことが分からないので、実際にためしてみた。やってみる
Management Console から インスタンスウィザードを起動して、"Step 4: Add Storage"のところで、"Add New Volume" を連打した。"/dev/sdb" からはじまり、"/dev/sdz" を通り過ぎて "/dev/xvdz" が表示されたあたりで、このあたりで許してあげようと思い "Launch Instance"。
結果
一見インスタンス自体は問題なく起動しようとしているように見える。がいつまでたってもSSHログインできない。get system log をみると以下のように、Bug を踏んでいた。
4394230.182195] kernel BUG at fs/sysfs/group.c:65!
[4394230.182198] invalid opcode: 0000 [#1] SMP
[4394230.182203] Modules linked in:
[4394230.182207] CPU: 0 PID: 19 Comm: xenwatch Tainted: G W 3.10.35-43.137.amzn1.x86_64 #1
[4394230.182215] task: ffff88002492c710 ti: ffff880024936000 task.ti: ffff880024936000
[4394230.182219] RIP: e030:[<ffffffff811eb772>] [<ffffffff811eb772>] internal_create_group+0x202/0x230
[4394230.182228] RSP: e02b:ffff880024937c50 EFLAGS: 00010246
[4394230.182232] RAX: 0000000000000400 RBX: ffff880003544000 RCX: 0000000000000000
[4394230.182236] RDX: ffffffff8184dfc0 RSI: 0000000000000000 RDI: ffff880003544080
[4394230.182241] RBP: ffff880024937c88 R08: 00000000000163c0 R09: ffff8800260163c0
[4394230.182245] R10: ffffea0000927d00 R11: ffffffff81311bb2 R12: ffff880003590000
[4394230.182250] R13: ffffffff8184dfc0 R14: 0000000000000000 R15: ffff880003544070
[4394230.182259] FS: 0000000000000000(0000) GS:ffff880026000000(0000) knlGS:0000000000000000
[4394230.182264] CS: e033 DS: 0000 ES: 0000 CR0: 000000008005003b
[4394230.182268] CR2: 0000000000000000 CR3: 000000000180c000 CR4: 0000000000002660
[4394230.182273] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[4394230.182277] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[4394230.182281] Stack:
[4394230.182284] ffff880003544080 ffffffff81256951 ffff880003544000 ffff880003590000
[4394230.182291] ffff880003544000 ffff880003544070 ffff880003544070 ffff880024937c98
[4394230.182298] ffffffff811eb7b3 ffff880024937ca8 ffffffff810f84b4 ffff880024937ce8
[4394230.182305] Call Trace:
[4394230.182311] [<ffffffff81256951>] ? kobj_kset_leave+0x51/0x60
[4394230.182316] [<ffffffff811eb7b3>] sysfs_create_group+0x13/0x20
[4394230.182324] [<ffffffff810f84b4>] blk_trace_init_sysfs+0x14/0x20
[4394230.182331] [<ffffffff8123ecfd>] blk_register_queue+0x3d/0x110
[4394230.182336] [<ffffffff81245a0d>] add_disk+0x1cd/0x4a0
[4394230.182341] [<ffffffff81324a1d>] blkback_changed+0xd3d/0x1010
[4394230.294407] [<ffffffff812da098>] xenbus_otherend_changed+0x98/0xa0
[4394230.294418] [<ffffffff812dc083>] backend_changed+0x13/0x20
[4394230.294433] [<ffffffff812d9436>] xenwatch_thread+0xb6/0x170
[4394230.294440] [<ffffffff81070e10>] ? wake_up_bit+0x30/0x30
[4394230.294454] [<ffffffff812d9380>] ? unregister_xenbus_watch+0x230/0x230
[4394230.294462] [<ffffffff8106fee0>] kthread+0xc0/0xd0
[4394230.294477] [<ffffffff8106fe20>] ? kthread_create_on_node+0x120/0x120
[4394230.294485] [<ffffffff8144a12c>] ret_from_fork+0x7c/0xb0
[4394230.294498] [<ffffffff8106fe20>] ? kthread_create_on_node+0x120/0x120
[4394230.294503] Code: 8b 7d d0 89 4d c8 e8 8e e7 ff ff 4c 8b 65 d0 8b 4d c8 e9 28 ff ff ff 4c 8b 65 d0 e9 1f ff ff ff 48 83 7f 30 00 0f 85 3e fe ff ff <0f> 0b b8 ea ff ff ff e9 29 ff ff ff be c3 00 00 00 48 c7 c7 ff
以下のようなログも出力していたので、多分デバイス名の付け方に問題があったのだろう。
[4394230.181916] WARNING: at fs/sysfs/dir.c:530 sysfs_add_one+0xa5/0xd0()
[4394230.181921] sysfs: cannot create duplicate filename '/class/block/xvdt'
[4394230.181925] Modules linked in:
[4394230.181931] CPU: 0 PID: 19 Comm: xenwatch Not tainted 3.10.35-43.137.amzn1.x86_64 #1
[4394230.181937] 0000000000000009 ffff880024937b50 ffffffff8143c559 ffff880024937b88
[4394230.181945] ffffffff8104bac1 00000000ffffffef ffff88000358acb0 ffff880024937c38
[4394230.181961] ffff880024aad000 0000000000000001 ffff880024937be8 ffffffff8104bb2c
[4394230.181969] Call Trace:
[4394230.181986] [<ffffffff8143c559>] dump_stack+0x19/0x1b
[4394230.181995] [<ffffffff8104bac1>] warn_slowpath_common+0x61/0x80
[4394230.182000] [<ffffffff8104bb2c>] warn_slowpath_fmt+0x4c/0x50
[4394230.182015] [<ffffffff811e9955>] sysfs_add_one+0xa5/0xd0
[4394230.182020] [<ffffffff811ea5a5>] sysfs_do_create_link_sd+0x105/0x200
[4394230.182026] [<ffffffff811ea6c1>] sysfs_create_link+0x21/0x40
[4394230.182041] [<ffffffff81311de4>] device_add+0x3e4/0x6d0
[4394230.182047] [<ffffffff81310517>] ? dev_set_name+0x47/0x50
[4394230.182061] [<ffffffff812459fd>] add_disk+0x1bd/0x4a0
[4394230.182068] [<ffffffff81324a1d>] blkback_changed+0xd3d/0x1010
[4394230.182084] [<ffffffff812da098>] xenbus_otherend_changed+0x98/0xa0
[4394230.182091] [<ffffffff812dc083>] backend_changed+0x13/0x20
[4394230.182097] [<ffffffff812d9436>] xenwatch_thread+0xb6/0x170
[4394230.182110] [<ffffffff81070e10>] ? wake_up_bit+0x30/0x30
[4394230.182117] [<ffffffff812d9380>] ? unregister_xenbus_watch+0x230/0x230
[4394230.182124] [<ffffffff8106fee0>] kthread+0xc0/0xd0
[4394230.182137] [<ffffffff8106fe20>] ? kthread_create_on_node+0x120/0x120
[4394230.182145] [<ffffffff8144a12c>] ret_from_fork+0x7c/0xb0
[4394230.182157] [<ffffffff8106fe20>] ? kthread_create_on_node+0x120/0x120
まとめ
AWS 的には、EBSを何個つけても問題なさそうだが、実際にたくさんEBSを付ける場合にはいろいろ考慮が必要なようだ。
